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AGRICULTURAL BOTANY
AGRICULTURAL BOTANY
THEORETICAL AND PRACTICAL
BY
JOHN PERCIVAL, M.A., Sc.D., F.L.S.
EMERITUS PROFESSOR OP AGRICULTURAL BOTANY
THE UNIVERSITY, READING
EIGHTH EDITION
DUCKWORTH
3 HENRgETTA STREET, LONDON, W.C.2
First Edition . . . .
Second Edition ....
Third Edition ....
Fourth Edition (ist Impression)
Fourth Edition (2nd Impression)
Fifth Edition (Revised) .
Sixth Edition (Revised) .
Seventh Edition (Revised)
Eighth Edition (Revised) .
Eighth Edition (2nd Impression)
Eighth Edition (jrd Impression)
Eighth Edition (4th Impression)
Eighth Edition (5th Impression)
Eighth Edition (Oth Impression)
Eighth Edition (?th Impression)
May 1900
March 1902
October 1907
March 1910
April igi3
September 1918
January ig2i
January 1926
January 1936
July 1942
November 1943
April 1945
March 1946
June 1947
March 1949
All Rights Reserved
Made and Printed in Great Britain by
Thomas Nelson 6- Sons, Ltd., Parksiae, Edinburgh
PREFACE
PRACTICAL men and the agricultural press have from time . to s
time complained of the absence of text-books of botany suitea
to the wants of the student of agriculture, those in existence
being works which treat^the subject from a purely scientific
standpoint and contain a large amount of matter which, though
important to the botanist, is nevertheless of little interest or
value to the agriculturist whose time for training in such matters
is necessarily limited.
The recent growth of interest in technical instruction, which
has resulted in a large increase in the number of colleges and
schools for agricultural education,' has rendered it imperative
that so serious a defect should be remedied, and this I have
endeavoured to do by writing the present volume.
The contents are based upon many years' experience in teaching
and lecturing to students, practical farmers and gardeners, and
embrace all those botanical matters which such experience has
led me to consider essential to a sound working knowledge of
the general principles of the science and its more immediate
application to the crops of the farm.
Although the book has been primarily written for the benefit
of students of agriculture, the greater portion of it is iqually
well adapted to meet the requirements of gardeners and all who
desire to obtain an insight into the general structure and life-
processes of plants, a knowledge of which must undoubtedly
conduce to a more satisfactory and economical management of
all cultivated plants.
Un|il quite recently botanical knowledge has apparently
been 'deemed of little importance in examinations in the
science and practice of agriculture, the science of botany
being usually treated as an * optional subject/ It is, how-
ever, gratifying to note that in the new regulations for the
examination for the National Diploma in the science and practice
of Agriculture, issued by the National Agricultural Examination
Board, Botany takes its proper place as an obligatory subject
beside its sister science Chemistry.
VI PREFACE
All the drawings in the work are original, and witri the excep-
tion of the diagrammatic figures have been made by the author
from living or natural examples. The panicles or ' ears ' of the
grasses are all drawn the natural size of average specimens,
in order that the figures may be of use in the identification
of these important plants.
The farm seeds are also drawn to a uniform scale ; their rela-
tive sizes may therefore be seen at a glance.
In this as in all scientific study, practical work is absolutely
essential to 4 proper understanding of the subject ; in recognition
of the importance of such work I have introduced into the text
of the volume a series of exercises and experiments, illustrative
of the principles and facts to be studied. These and others,
which will suggest themselves to intelligent students, should be
attacked and carried out in the spirit of research, so that students
may learn to observe, record and discover things themselves.
In conclusion, I tender my sincere thanks to my colleague
Mr Cousins, and also to Mr W. H. Hammond, Milton Chapel,
Canterbury, and Dr A. B. Rendle, of the British Museum
(Natural History Department), for valuable criticism and assist-
ance in reading through the proofs.
JOHN PERCIVAL.
SOUTH-EASTERN AGRICULTURAL COLLEGE,
WYE, KENT.
March, 1900.
PREFACE TO THE SECOND EDITION
THE very appreciative reception and rapid sale of the first edition
have pfoved that a real want has been met by the book.
The present edition has been emended and revised throughout
in accordance with recent work and the criticisms of botanical
friends.
I shall be grateful for any further suggestions which may be
deemed necessary to render the work more complete for educa-
tional purposes or more useful to the student of this and allied
branches of applied botany.
JOHN PERCIVAL.
Nov. 1901,
PREFACE Vll
PREFACE TO THE FOURTH EDITION
To this edition a new chapter has been added and very consider-
able additions made throughout the work, with a view of improving
its usefulness and keeping the matter up to date.
It is gratifying to find that the volume is highly appreciated
by teachers and students in all countries wherever English is
spoken.
JOHN PERCIVAL.
Jan. 1910.
PREFACE TO THE FIFTH EDITION
A CHAPTER on the Polygonacese has been added and other
parts revised and emended.
JOHN PERCIVAL.
Sept. 1918.
PREFACE TO THE SIXTH EDITION
THE work has been revised throughout.
JOHN PERCIVAL.
Die. 1920.
PREFACE TO THE EIGHTH EDITION
THE text has been revised throughout, and additions made to
chapters ix and xxii.
JOHN PERCIVAL.
THE UNIVERSITY, READING.
Nov. 1935.
CONTENTS.
PART I.
GENERAL EXTERNAL MORPHOLOOY.
CHAFTKX *AGB
I. INTRODUCTORY . . i
II. SEEDS: THEIR STRUCTURE AND GERMINATION . 7
The common bean, j \ White mustard, 16 ; Onion, 19 ; Wheat, 22.
III. THE ROOT ..... r 25
Primary and secondary roots, 25 ; Adventitious roots, 28 ; Root-
hairs, 32.
IV. THE VEGETATIVE SHOOT : STEMS, LEAVES AND BUDS 34
Buds, 37 ; Branching of stems, 40 ; Twigs of trees in winter, 42 ;
Spurs, 44 ; Dormant buds, 50 ; Adventitious buds, 51 ; Stems
and their varieties, 52 ; Recognition of trees by means of twigs in
winter, 6z.
V. THE LEAF. . 63
Foliage-leaf, 68 ; Modified leaves, 72 ; Leaf-arrangement, 74 ;
Bud-arrangement, 76 ; Leaf-fall ; Evergreens, 76.
VI. THE FLOWER ... 78
Arrangement, symmetry and number of floral leaves, 80; The
receptacle, 81 ; Non-essential parts of the flower; perianth, 83;
The Calyx, 83 ; The Corolla, 83 ; The essential parts of the flower,
. 83 ; The Androecium, 84 ; The Gynaecium, 85 ; Placentation, 87 ;
Monoclinous and diclinous flowers; monoecious and dioecious
plants, 87.
VII. THE INFLORESCENCE .... 89
Racemose inflorescences, 89; Cymose inflorescences, 92; Mixed
inflorescences, 93.
VIII. THE FRUIT: DISPERSAL or SEEDS . . 95
Indehiscent dry fruits, 96 ; Schizocarps, 97 ; Dehiscent dry fruits,
97 ; Succulent or fleshy fruits, 99 ; Dispersal of seeds, ico.
ix
Xll CONTENTS
CHAFTKX FACB
XXV. CANNABACEJE . . . . 332
The Japanese Hop, 333 ; The common Hop, 339 ; Hemp, 348.
XXVI. POLYGON ACK^E . . . . 350
General character of the Order, 350 ; Common Buckwheat, 351 ;
Tartarian Buckwheat, 355.
XXVII. CHENOPODIACB-* . . . . 356
Sea Beet, 357; Common Beet, 357 ; Mangel Wurzel, 358 ; Sugar-
Beet, 367.
XXVIII. CRUCIFEIUE .- . . . .371
Wild Cabbage, 373 ; Cultivated cabbage and its varieties, 373 ;
Turnip, 377 ; Swede, 381 ; Rape, cole or coleseed, 385 ; Black
mustard, 387 ; White mustard, 389 ; Charlock, 391 ; Wild Radish,
392.
XXIX. LINAGES " 395
General character! of the Order, 395 ; Flax or Linseed, 395.
XXX. ROSACES . . . ^ . . .403
Plums and Cherries, 403 ; Sloe, Bullace, Wild Plum and Apricot,
405; Dwarf Cherry, Gean, Bird Cherry, Almond, Peach, 406;
Strawberries, 407 ; Raspberry and Blackberry, 409 ; Dog Rose, 410 ;
Pear, 411; Apple, 412; Medlar, Whitethorn and Quince, 413;
Lesser Burnet, 414.
XXXI. LEGUMINOS^:^ . . . .416
Peas, 418 ; Bean, 422 ; Vetch, 424 ; Vetchling, 426 ; Red clover,
437 ; Zig-zag clover, 431 ; Alsike, 431 ; White clover, 431 ; Crimson
clover, 432 ; Yellow suckling, 434 ; Hop clover, 434 ; Black medick,
435 ; Lucerne, 435 ; Melilot, 438 ; Sainfoin, 438 ; Serradella, 440 ;
Kidney Vetch, 440 ; Bird's- foot trefoil, 441 ; Gorse, 443 ; Rest-
Harrow, 443 ; Lupins, 443.
XXXI L UMBELLIFER/E . . . . .447
Wild carrot, 450 ; Cultivated Carrot, 450 ; Parsnip, 458 ; Hemlock,
460 ; Water Hemlock or Cowbane, 460 ; Water Dropwort, 461 ;
Fool's Parsley, 461.
XXXIII. SOLAN ACEA ^ 462
Potato, 463 ; Bitter-Sweet, 474 ; Black nightshade, 474 ; Deadly
nightshade, 474 ; Henbane, 475.
XXXIV. COMPOSITE < 476
General characters of the Order, 476; Yarrow: Millefoil or
Thousand-leaf, 479-
XXXV. GRAMINE^L. TRUE GRASSES . . .481
CONTENTS Xiii
CHAPTER PACK
XXXVI. GRAMINEA (continued). CEREALS . .489
XXXVII. CULTIVATED AND WILD OATS (Genus Avcna) . 499
Wild Oat, 499 ; Bristle-pointed Oat, 500 ; Animated or Fly Oat,
500 ; Short Oat, 500 ; Common Cultivated Oats, 500.
XXXVIII. CULTIVATED BARLEYS (Genus Hordeum) . 506
Cultivated Barleys, 507 ; Distinguishing features of Barley-grains,
512 ; Characters of a good malting barley, 514.
XXXIX. CULTIVATED RYE (Genus Secale) . . .518
XL. CULTIVATED WHEATS (Genus Triticum) . 521
XLI. COMMON GRASSES OF THE FARM . . 536
XLII. GRASSES AND CLOVERS FOR TEMPORARY AND
PERMANENT PASTURES . . . 564
Grasses and clovers for leys of one, two or three years' duration,
566 ; Grasses and cloves for temporary pastures lasting from three
to six years : Grasses and clovers for permanent pasture, 569 ;
Weight of seed to be used, 577.
PART V.
WEEDS OF THE FARM.
XLI 1 1. WEEDS: GENERAL . . . 579
Their injurious effects, 579 ; Mistletoe, 583 ; Duration of weeds,
585 ; Habit of growth of weeds, 587 ; How weeds are spread, 588 ;
Extermination of weeds, 590.
XLIV. WEEDS: SPECIAL ... -597
Weeds of arable ground, 597 ; Weeds of pastures, 6xa.
PART VI.
FARM SEEDS.
XLV. FARM SEEDS: GENERAL . . . .622
Purity, 624 ; Germination capacity, 628 ; Speed of germination
or germination energy, 634; Weight, 637; Form, colour, bright-
ness and smell, 643.
XLV I. FARM SEEDS: SPECIAL . , . 647
XIV CONTENTS
PART VII.
FUNGI, CONSIDERED CHIEFLY IN RELATION TO SOME
OOMMON DISEASES OF PLANTS.
CHAPTER PAGE
XLVII. FUNGI: GENERAL . . . . .687
Hypba and mycelium, 687 ; Reproduction, 689 ; Germination of
spores, 692 ; Mode of Life : Saprophytes and Parasites, 693 ; General
advice to be followed when dealing with plant diseases, 696.
XLVII I. FUNGI (continued) PHYCOMYCETES . . . 698
Eumycetes, 698 ; Phycomycetes (sub-class i. Zygomycetes), 699.
XLIX. FUNGI (continued) PHYCOMYCBTES . . .702
Phycomycetes (sub-class ii. Oomycetes), 702 ; Damping-off, 703 ;
Potato diseases, 707.
L. FUNGI (continued) BASIDIOMYCBTES . . 725
' Smut ' of Oats, 726 ; ' Smuts ' of wheat, barley and rye, 728 ;
Bunt of wheat, 733 ; Rust and mildew of wheat, 736 ; Other species
of rusts, 745 ; The common mushroom, 750.
LI. FUNGI (continued) ASCOMYCETES . 755
Yeasts, 756 ; Mildews, 758 ; Ergot, 768.
LI I. * CLUB-FOOT* DISEASE . . . .773
PART VIII.
BACTERIA,
LI 1 1. BACTERIA: THEIR MORPHOLOGY AND REPRODUC-
TION . . . . . .779
Forms of Bacteria, 779 ; Vegetative reproduction, 780 ; Reproduc-
tion by means of spores, 781 ; Conditions affecting development,
784 ; Sterilisation and pasteurisation, 786.
LIV. BACTERIA: THEIR WORK . . . .789
Lactic fermentations, 790; Butyric fermentations, 792; Acetic
fermentations, 794 ; Fermentation of cellulose, 795 ; Fermentation
of urea, 796 ; Putrefaction, 797 ; Nitrification, 799 ; Denitrification,
8oa; Fixation of free nitrogen, 803; Bacteria and diseases of
animals, 813 ; Diseases of plant! caused by bacteria, 8x5 ; Black
rot of cabbages, 816.
PART I.
GENERAL EXTERNAL MORPHOLOGY.
CHAPTER I.
INTEODUOTORY.
i. THE things met with every day can be separated into two dis-
tinct classes or groups, namely, those which are alive, such as
birds, insects, cattle, trees, flowers, and grasses, and those which
are never possessed of life, such as air, water, glass, and iron.
Although it is impossible to give a complete and satisfactory
account of what life is, for all practical purposes the difference
between the two classes of objects is easily recognised, and a
more extended study of them leads to the conclusion that between
the living and the inanimate world there is a hard and fast line
of separation.
The chief and most obvious peculiarity of living things is theii
power of giving rise to new individuals that is, their power of
reproduction. They are ordinarily separated into two classes,
namely animals and plants. The term Biology in its widest
sense is used to denote the study of all forms of living things,
that branch of it dealing with animals being known as Zoology,
while the science of Botany is concerned with the study of plants.
The most familiar animals have the power of moving about in
a way which is not possessed by plants. Moreover, the former
require as food, substances which have been derived from other
living things, such as flesh of all kinds, milk, bread, potatoes,
and similar materials ; while most common plants are capable of
utilising substances whxh belong entirely to the inanimate world,
2 INTRODUCTORY
such as carbon dioxide, water, and various minerals. Although
these points of difference between plants and animals . are
sufficient to separate the two classes from each other, so far as
the purposes of everyday life are concerned, it must be mentioned
that a further examination of living things shows that there are
some which in structure and power of utilising inorganic sub-
stances as food-materials resemble plants, but which are never-
theless able to move about as freely as animals, and that other
structures usually considered as animals move very little. Then,
again, there are living things always classed as plants, which pro-
duce flowers and seeds, although they cannot live when supplied
with carbon dioxide, water and minerals, but must be fed upon
the same or similar substances to those needed by animals.
Indeed, all attempts to draw a hard line of separation between
plants and animals are found to end in failure. The living sub-
stance within them appears to be the same, and between the so-
called animal and vegetable kingdoms there is no distinct point
of difference. The living world is essentially one, and not two,
and it is very necessary to constantly bear in mind that plants
are just as much living structures as animals are, since by far the
larger number of mistakes in the management and cultivation of
plants are due to want of proper appreciation of this fact
2. For the present our attention will be confined to the common
plants of the farm and garden. In form and structure these
are altogether different from animals, and as the difficulty of
defining the two classes of living things is only met with in
studying minute and practically unseen organisms it may be
dismissed for the present.
It will be readily understood that plants may be studied from
a great many different points of view, and consequently special
branches or divisions of the science arise. Attention may be
confined to an investigation of the uses of the various parts of a
plant's body to the work which the leaves, roots, and flowers
perform in the life of the plant ; this part ef the subject is known
INTRODUCTORY 3
as physiology. Another branch is concerned with the form,
origin, development, and relationship of the various parts to
each other, without any reference to the work they do : the term
morphology is used to denote this division of the science.
Then, again, the structure and arrangement of the various parts
of plants may be studied in order to determine their points of
similarity and of difference with a view of placing together in
groups all those possessing certain degrees of resemblance : this
is usually termed Systematic Botany. For purposes 'of con-
venience and methodical extension of knowledge of the subject
many other divisions of the Science are made, and in each of
them the study of plants is made from a somewhat different
standpoint. Although other classes of the vegetable kingdom
need attention it is advisable to confine our study at first to the
seed- bearing plants, as this division includes all those which are
everywhere most familiar. It is essential that farmers and all
who are interested in the management of plants for pleasure or
profit should examine and investigate them from as many differ-
ent aspects as possible, as only by so doing can real progress be
made in their cultivation.
3. Most plants of the farm belong to the class known as Sper-
matophytcsw seed-bearing plants; the latter are sometimes called
Flowering plants or Phanerogams, but their chief characteristic is
the production of seeds. The life-history of a spermatophyte is
a continuous process of development or unfolding of parts in
which we may recognise four fairly distinct periods, namely :
(1) Germination of the seed and the escape of a young plant
from it ;
(2) The development and growth of roots, stems, and green
leaves ;
(3) The flowering period or formation and opening of flowers \
and
(4) The production and ripening of fruits with their contained
seeds.
4 INTRODUCTORY
The succession of events is generally in this order, and usually
the formation and unfolding of roots, stems, and leaves occupies
by far the greatest portion of the plant's life.
There is, however, great variation in the time taken to
reach the several stages of development, and the periods
are not always of the same duration in the same species of
plant.
4. So far as their total duration of life is concerned, plants
may be usefully divided into annuals^ biennials^ and peren-
nials.
By an annual is meant a plant which completes its life-history
in one growing season. Starting as a seedling in spring or early
summer, it develops root, stem, and leaves, and then produces
flowers and seeds, after which it dies, leaving behind it offspring
in the form of seeds. The time taken by annuals to reach the
stage of seed-production is not always the same ; usually the
whole of the season, from spring to autumn, is necessary, and
only one generation is produced in that time. Some of them,
however, termed ephemerals, such as chick weed and groundsel,
produce seeds in a few weeks, and these may germinate and pro-
duce a second and third crop of plants before frost cuts them
down in autumn and winter.
Biennials^ beginning life as seedlings in spring or summer,
occupy the first growing season in the production of root, stem,
and leaves only. They then rest during winter, and in the
following year start growth again, and produce a stem bearing
flowers and seeds, after the ripening of which the plant dies.
Wild carrot, parsnip, and some varieties of thistles behave in this
manner.
Perennials are plants which live more than two years, and
often several seasons elapse before flowers and seeds are produced.
They are frequently divided into two classes, namely, (i) herbaceous
perennials and (2) woody perennials. In the former the leaves
and stems above ground are of a soft nature and die down at the
INTRODUCTORY >
cna 01 me growing season, the parts of the plant which still
remain to carry on growth in subsequent years being under-
ground : the stinging nettle, hop, and potato are representa-
tives of this class. In woody perennials, of which all trees
and shrubs are examples, the stems above ground are hard
and woody.
This method of dividing plants according to their length of
life, although useful, is by no means a strict one, as the duration
is dependent to some extent upon season, time of sowing, and
the treatment which they receive. Wheat, for example, if sown in
early spring behaves as an annual, but if sown in late summer or
autumn does not perfect its seed and die until the following
year. If kept continually cut or cropped down by animals it
may even remain two years or more without dying, especially when
thinly sown on good soils and allowed plenty of room for branch-
ing. Annual mignonette of gardens is often made to last several
years in pots by pinching off the flowering stems as soon as they
begin to form.
Turnips and other plants, usually biennials in ordinary farm
practice, are invariably annuals if sown early in the year, say in
February.
Climate and soil also influence the duration of plants, annuals
in some districts becoming biennial or even perennial in others.
Ex. 1. Sow short rows ot the cereals and 'roots' mangels, turnips,
swedes and carrots on the first day of each month during a whole year, and
make careful observations and notes on their subsequent growth up to the time
of seed production. Interesting and useful results are obtained.
5. As the duration of flowering plants is subject to such varia-
tion and their classification into annuals, biennials, and peren-
nials, consequently somewhat arbitrary, they are sometimes
placed in groups according to the number of times they are able
to produce seeds.
Those which yield only one crop and then die are termed
6 INTRODUCTORY
monocarpic plants : annuals and biennials are of this nature, and
some perennials also.
Such plants as most trees and shrubs, thistles, bind-weed,
coltsfoot, and many grasses which are able to produce flowers
and seeds during an indefinite number of seasons are described
as polycarpic.
CHAPTER II.
SEEDS: THEIR STRUCTURE AND GERMINATION.
i. IT is well known that one of the most ordinary methods of
raising plants is to sow what are called seeds, yet how few there
are among the many who use them who fully appreciate their
real nature and capabilities. This want of knowledge is not due
perhaps so much to want of interest in them, as to the fact that
for their proper management they are usually buried away in the
ground, and are therefore unseen ; moreover, many of them are so
small that their structure is difficult to observe with the naked eye.
In order to understand the true nature of a seed it is neces-
sary to examine its origin and construction, and watch its
development as far as possible from the earliest stages to the
time when it gives rise to a completely formed young plant.
The Common Bean. A broad bean is one of the largest seeds
met with in ordinary farm or garden practice, and as its parts
are all sufficiently large to be observed without the special aid
of anything more than . ___
an ordinary pocket lens,
it is especially fitted for
study.
When a nearly ripe pod
of a broad bean plant is
opened, each seed within
it is found attached to
the inside by means Of FIG. i.- Piece of bean pod showing the funicle (/)
a short stalk or funicle and its attached seed '
(Fig. i), and it is through this stalk that all the nourishment
8 SEEDS ! STRUCTURE AND GERMINA~N
passes from the parent to enable the young seed to aeveiop. Ai
first the pod exists in a rudimentary form in the centre of a flower
and its parts and contents are very small ; they are nevertheless
readily seen with a pocket lens. After the fading of the flower,
the pod and seeds within it grow larger and larger at the expense
of food supplied by the rest of the plant, and ultimately when
ripe the funicles wither and dry up, and the seeds become de-
tached from the parent which has produced them.
When dry and ripe each bean seed is hard, with an uneven
surface, but its internal construction cannot be clearly examined
in this condition. On soaking in water for twelve hours,
however, it becomes softer, and the parts can then be easily
investigated.
The outside, which is a pale buff colour, is smooth, and has at
one end a narrow elongated black scar called the hilum of the
seed. It is known popularly as the ' eye ' of the bean, and marks
the place where the broad end of the funicle separated from the
seed when it ripened in the pod.
Quite close to one end of the hilum is a very minute hole
known as the micropylt, easily seen with a lens, and through
which water oozes out usually accompanied by bubbles of air
when soaked beans
are squeezed be-
~C tween the finger and
thumb. This open-
ing communicates
with the interior of
the seed, and is the
only one it possesses.
FIG. a. Bean embryo, show- FIG. 3. The same as Fig. 2, Qn slitting TOUnd
ing (r) radicle and (c) after removal of one coty- > &
cotyledon. ledon ; r radicle ; b the the edge with a knife.
plumule ; c cotyledon of '
embryo. the outer part of the
bean can be stripped off as a pale, semi-transparent, leathery
membrane ; this is known as the testa or sed-coat, and is thickest
THE COMMON BfiAN 9
and of softest texture where the hilum is situated The rest of
the seed after the testa is removed, is of oval flattened shape
similar to the complete bean, and is divisible into two large
fleshy halves called cotyledons (Fig. 3, *), which, however, are not
completely separate from each other, but connected at the side
with a conical projecting body (Fig. 3, r) y one end of which is
found to fit into a hollow cavity in the seed-coat exactly opposite
the micropyle ; the other end is bent and turned inwards between
the fleshy cotyledons. The extent and shape of this small curved
structure is most easily observed when one of the cotyledons is
removed completely ; it remains attached to the other as in Fig. 3.
Ex. 2. Soak some broad beans in water and keep them in a warm place
all night. Examine them next day and make drawings of the various parts
seen both before and after stripping off the testa. Observe the relative
position of the parts of the embryo in reference to each other and to the
seed-coat.
Examine and compare the structure of the following seeds after soaking in
the same way : Pea, scarlet runner beans, vetches, and red clover.
The bean seed contains nothing more than what has already
been described ; the nature and relationship of its component parts
only become intelligible when the seed is placed in the ground
or maintained under certain conditions, and allowed to grow.
When growth commences the lower end of the small curved
structure (Fig. 3, r) elongates and breaks its way through the
coat of the seed at a point very close to the micropyle, but
not, as often erroneously stated, through the micropyle itself.
It soon assumes the form seen in Fig. 4, and is recognised as a
root of a young bean plant The upper bent half, which lies
between the cotyledons, also pushes its way out of the same
opening in the seed-coat and develops into a stem, from the
tip of which leaves are gradually unfolded. It is thus seen
that the seed of a broad bean is a packet containing a bean
plant in a rudimentary condition.
This plantlet is callai an embryo, and the portion of it which
10 SEEDS I STRl/CTURE AND GERMINATIQN
becomes root and stem is its primary axis. The part of the
primary axis which is below the point where the cotyledons
are attached consists of a very small piece of stem, the hypocotyl^
at the end of which is the radicle or primary root. Where
the stem ends and the root
begins cannot be determined
in the bean seedling without
the aid of the microscope and
i examination of the internal
structure of the axis of the
plant.
The curved end of the
primary axis above the cotyle-
dons is the plumule of the
embryo, and consists of a
very short piece of stem,
the epicotyl on the top of
which is a bud. From the
latter is derived the ordinary
stem which comes above
ground with its green leaves
and flowers.
In the early stages of the
growth of the embryo from
the seed the hypocotyl grows
very little, the part of the
FIG. 4. Bean embryo after four days' growth. . .
One cotyledon has been removed. <:Coty- Stem which grOWS HlOSt being
ledon ; r primary root ; b epicotyl with . . . _ .
bud at its tip. the epicotyl. It is on account
Compare with Fig. 3. ,. . . . .. , .
of the elongation of this
portion of the plantlet that ttye plumule with its young leaves
are driven above ground, the cotyledons remaining below en-
closed within the seed-coat.
The upper part of the stem bearing the plumule comes out of
the seed bent, as in Fig. 4, and it maintain^ this curved shape for
THE COMMON rfEAN II
some time after emerging. By this behaviour the delicate
leaves of the plumule are protected from injury during their
progress upwards when a seed is sown in earth or sand.
Ex. 3. Fold up some soaked beans in two thicknesses of white flannel
made damp, and place them on a plate. Cover them with another plate
placed upside down, and leave them in a warm room. Examine them twice
a day, leaving them, exposed to the fresh air for a few minutes each time,
and keeping the flannel damp, not wet. When they sprout notice the place
where the radicle has come out of the seed-coat. Let some grow till the
radicle and plumule are well out of the seed, and compare the various parts
of the sprouted seeds with unsprouted ones.
2. GERMINATION. When the pod of the bean is developing, the
embryo in the seed is being fed by the parent and visibly grows
until ripeness is attained. The young plant then assumes a dor-
mant or resting state within the seed without showing any signs
of life. Under certain conditions, however, the plantlet begins
to wake up, and soon escapes from its protective coat to lead
a separate and independent life. This awakening from a resting
condition to a state of active growth is called germination^ and
is dependent upon an adequate supply of (i) water, (2) heat,
and (3) air or oxygen. It is also essential, of course, that the
plantlet in the seed must be alive.
The exact nature of the dormant state of seeds is not
understood, but in old seeds and those which are gathered
in an immature condition or badly stored the embryo is often
weakened or actually dead ; in the latter case no germina-
tion is possible. The exact length of time which seeds may
be kept before death of the embryo takes place has never
been satisfactorily determined; it varies with the species
of the seed, its ripeness and composition, and also with the
method of storage. In the case of most farm and garden seeds
kept in the ordinary way, few of them are found capable of growth
after ten years, and a large number die in two or three years, but
on this point more will be said in a later chapter. For present
purposes it will suffice merely to mention that age is a deter-
12 SEEDS I STRUCTURE AND GERMINATION
mining factor in the germination of seeds, apart from the three
conditions previously mentioned.
3. That water is necessary is well known, as beans may be kept
indefinitely in a sack or drawer at various temperatures and with
access to air without germination taking place. When placed in
moist ground, or between damp blotting-paper, they absorb
water very readily. This is most easily observed when beans are
soaked for twelve hours in a dish containing water. The water
is transmitted through all parts of the coat, but much more
quickly and easily through the micropyle and the line of softer
material which runs the whole length of the centre of the hilum.
It is rapidly brought into contact with the part of the embryo
which grows first, namely, the radicle. The soft spongy
thicker part of the inside of the testa lying beneath the hilum
stores up a considerable amount of water for the benefit of the
developing plant, and the whole of the embryo and the seed-
coat absorb water and become softer and larger in consequence ;
it is only after this swelling has happened that a bean begins to
show any signs of germination.
Ex. 4. To show the influence of the micropyle and hilum in the absorp-
tion of water, take twenty beans all as near the same size as possible. Paint
over the micropyle and hilum of ten of them with quick -drying varnish 01
1 cycle black ' ; on the other ten paint streaks of the same size on the sides
of the seeds, leaving the micropyle and hilum untouched. Weigh both lota
separately, and place them together in a basin of water all night. Take
them out next morning, dry them carefully with a towel, and weigh again,
and see which lot has increased most.
4. The need of an adequate temperature for germination is a
matter of common knowledge among those accustomed to sow
seeds. If soaked beans are placed in the ground in midwinter
they show little or no signs of waking from their dormant con-
dition, yet when placed under a glass on damp blotting-paper
indoors, the radicle makes its exit from the seed in a few days.
Seeds differ in the temperature which is necessary to induce
them to germinate, the embryos in som# commence to extend
THE COMMON BEAN 13
their radicles and push their way through the seed-coat even if
just kept above freezing point ; others require a temperature of
9 or 10 C. to start growth. If attempts are made to grow beans
at 45 C. it will be found to be too hot, and they make little or
no progress. Between this high temperature at which growth
appears impossible, and the freezing point where the develop-
ment of the embryo of the bean is also suspended, there is a
temperature at which the embryo makes the most rapid progress,
and emerges from the seed-coat in the shortest possible time ;
this most favourable temperature is about 28* C., both above it
and below it the germination of the bean is retarded.
Ex. 5. Arrange two separate lots of similar-sized beans soaked for the
same length of time in damp flannel as described in Ex. 3, and place one
in a warm kitchen and the other in a cold cellar. Observe which show
their radicles first.
5. The supply of fresh air is also an essential condition for growth
of the young plant from the bean seed, but the evidence for its
need is not so manifest or so generally recognised as the necessity
for moisture and warmth. It will be found, however, when
beans are placed in a flask or bottle containing carbon dioxide or
hydrogen gas they refuse to germinate, even when they are sup-
plied with a proper amount of water, and kept at summer heat
Ex. 6. Place ten soaked beans in a wide-necked bottle. Fill the bottle
with carbon dioxide gas or coal gas, and cork it up with a tightly-fitting
indiarubber stopper.
Arrange another bottle in the same way, but with ordinary air in it instead.
Take out the stopper of this one twice daily and blow in fresh air, so as to
ensure a good supply to the seeds. Place both in a warm situation and
observe which germinate best.
6. The peculiar extension or growth of the parts of the interior
of the bean seed, and the fact that a suitable supply of water, air
and heat is necessary for the manifestation of these changes,
suggests to us that we are dealing with a living structure. This
becomes all the moreapparent when we observe that the oxygen
14 SEEDS: STRUCTURE AND GERMINATION
of the air is absorbed, and in its place carbon dioxide is given off
into the surrounding air, for this is what happens in the breathing
of a living animal.
Bac. 7. Carbon dioxide is produced when beans germinate. Place twenty
soaked beans in a wide-mouthed bottle, and cork them up after showing that
a match burns freely in the bottle. Leave them in a warm place for twenty-
four hours, and try if a match will now burn in the bottle.
The carbon dioxide gas can be poured out into a beaker containing lime
water; on shaking, its presence is proved by the lime water becoming
c milky ' owing to the precipitation of carbonate of lime.
The particular use of the water, heat and air to the plant we
cannot at present discuss. It may, however, be mentioned that
without water the embryo would have little chance of becoming
free from the tough and hard seed-coat surrounding it; water
softens the latter, and makes it more easily torn by the extending
radicle and plumule.
In the early stages of the life of the bean plant, from the com-
mencement of germination up to the time when the first green
leaves are unfolded, the development and building up of the
elongating rootlet and shoot depend upon the thick cotyledons.
At first the latter are thick and fleshy, but as the radicle and
plumule grow the cotyledons become softer and thinner, ulti-
mately shrivelling considerably. The cotyledons are leaves, the
interior of which is packed with food for the rest of the growing
embryo, and a large amount of the water absorbed by the seed
is used for the purpose of dissolving the nutrient material in
them, and carrying it from them to the various parts of the root
and shoot of the young plant where growth is going on.
Ex. 8. Germinate beans in damp flannel a in Ex. 3, and show that the
cotyledons are essential to the development of the root and shoot of the em-
bryo by cutting them off as soon as the two latter parts have emerged from
the seed-coat. Try separating one cotyledon and then two at various stages
of development, and see if the axis (root and shoot) can be made to develop
without them. The growth should be allowed to continue some time in
order to obtain well-marked effects.
7. Not only do the changes observed innhe embryo of a ger-
THE COMMON flEAN 15
minating bean point to the conclusion that it is a living structure
and like an animal dependent on a proper supply of water, heat
and air for the manifestation of its life, but the parts of a young
bean plant after emerging from the seed soon give evidence of
the possession of peculiarities which are associated with life.
When put in the ground, the radicle, in coming out of the seed,
turns straight downwards and continues to grow in this direction.
This is the case no matter in what position the seed is placed.
If, after germination has commenced, it is taken and replanted
with the primary root pointing to the surface of the soil, the tip
of the root soon begins to curve downwards again, and will
maintain this course until again disturbed.
The plumule behaves in exactly the opposite manner ; after
emerging from the seed-coat its bent tip grows upwards and
away from the root; if the seed is reversed and replanted the
plumule begins to curve in such a manner that its tip is driven
upwards towards the surface of the ground. That these peculi-
arities are somehow connected with life is clear, as dead embryos
show no such behaviour.
Ex. 9. Sow soaked beans in a flower pot or box filled with ordinary garden
soil placing them in various positions in it, some laid on the flat side, some
with the hilum directed upwards, and others with the hilum downwards.
Allow them to grow in a warm place : take them up as soon as signs of germin-
ation are noticed, and observe the direction the root and shoot have taken.
The peculiar tendency for the root always to go downwards and stem
upwards can be investigated by sowing beans in ordinary garden soil and
afterwards reversing them. To avoid error all should be taken up, and
then placed again in the soil in various positions some as they were, a
few with their roots and stems reversed, and others laid in a horizontal
position. They may be re-examined at the end of a week.
Another method of showing the same peculiarity may be carried out
thus : Germinate soaked beans in damp flannel as in Ex. 3. When the
roots have extended about half an inch take two seeds and suspend them by
means of thread side by side in a bottle with their roots downwards and stem
upwards. The bottle should contain a little water to keep the air damp.
When the roots have grown about two inches reverse one of the seeds so that
its root points upwards tad stem downwards. Notice that the tip of the
16 SEEDS: STRUCTURE AND GERMINATION
root of the reversed seed in about twelve hours begins to turn downwards,
while the plumule more slowly bends in such a way as to assume the position
it had before it was reversed. The bottle should be placed in a dark box or
cupboard to avoid the influence of light on the plant, and fresh air should be
blown into the bottle twice a day.
8. Although seeds vary almost indefinitely in regard to size and
shape they are similar to the bean in so far as they all contain a
young plant packed away within the seed-coats. In this essential
feature all seeds agree with few exceptions, and it is on account of
the existence of a young plant within them that they are of use
in the raising of crops or plants.
The manner, however, in which the embryo is arranged, and
the relative size and appearance of its various parts, differ con-
siderably in seeds; moreover, the growth during and after
germination is not the same in all cases. A few of the more
important and common variations in these respects must be
noticed.
White Mustard. The seed of white mustard (Brassica alba
Boiss.) contains an embryo which like that of the bean consists of
a radicle, plumule and two cotyledons; the latter, which are
folded together, are relatively thinner than those of the bean and
deeply notched as in Fig. 5. The radicle is bent round and lies
in the fold of the cotyledons, between which is the very small,
almost invisible plumule.
On germination the cotyledons, instead of remaining within
the seed-coat and below the ground as in the case of the broad
bean, escape from the enclosing coats altogether and grow up
out of the ground, enlarging at the same time, and becoming
green like ordinary leaves. They are the first ' smooth ' leaves
of the seedling mustard plant
After a short time the plumule grows up from between the
cotyledons and forms a stem upon which are gradually unfolded
the ordinary divided ' rough ' leaves.
Bx. 10. Soak white mustard seeds, and examine their structure, noting
especially the way in which the embryos are packet in them. Allow some to
WHITE MUSTARD 17
germinate and grow for a week or more on damp flannel, and examine them
in various stages of development, noting the notched cotyledons with small
C
Fio. 5. x. Seed of White Mustard. 2. Folded embryo as seen after
removal of seed-coat. 3. The same unfolded. 4. Seed ger-
minating. 5. Young seedling. 6. Same as 5, but a week older.
c Cotyledons or 'smooth leaves'; h hypocotyl: r radicle and
primary root ; / first foliage leaf (' rough leaf') ; p petiole
of another leaf similar to / with blade removed ; b terminal
bud ; x surface of the soil.
plumule, well-marked hypocotyl, and distinct separation between the latter
and the root.
1 8 SEEDS: STRUCTURE AND GERMINATION
9. The term hypogean is applied to cotyledons which remain
below ground, those coming above being epigean, the relative
amount of growth in the hypocotyl and epicotyl determining
their position. If the hypocotyl grows vigorously during or
after germination the cotyledons are forced above ground ; when
only the epicotyl grows the plumule is lifted up above the soil,
but the cotyledons remain below where the seed is placed.
In the broad bean the hypocotyl is very short, and the point
where it ends and the root begins is not clearly denned. In a
mustard seedling, however, the point of separation between the
root and stem is somewhat swollen and readily distinguished
(Fig. 5).
10. All plants whose embryos, like those of the bean and
mustard, possess two cotyledons, are known as Dicotyledons j
they form a very large, well-marked class of the flowering or
seed-bearing plants.
n. The seeds hitherto mentioned contain within their coats
nothing but an embryo plant, which depends for the develop-
ment of its root and shoot upon the substances stored up in
some part of its body, its cotyledons chiefly. This is true even
in the case of seeds like those of white mustard, in which the
cotyledons of the embryo are comparatively thin. There are,
however, a number of plants, such as the ash, mangel and
potato, which, although belonging to the Dicotyledons, have
seeds in which there are stores of food inside the seed-coat,
but free from the embryo and its cotyledons (Fig. 109). Such
separate reserve-food is stored in that part of the seed known
as the endosperm or 'albumen, 1 and seeds in which it is pre-
sent are called endospermous or albuminous seeds. Those like
the bean, pea, and vetch, mustard, and turnip, which have
no separate reserve-food, are known as exendospermous or
exalbuminous seeds.
Ex. 11. Take out a seed from the fruit of the ash tree in autumn ; carefully
cut thin shavings from the flat side of the seed, starting about the middle of
ONION 19
the seed and cutting towards the narrow end. Note the white embryo with
its well-marked radicle, hypocotyl and two flat cotyledons lying within the
semi-transparent endosperm.
12. Some of the most commonly occurring endospermous
seeds will be found to have embryos within them which are not
dicotyledonous, and whose structure is in many respects very
different from those we have hitherto mentioned. A good
example is met with in the onion.
Onion. The seed is black, somewhat oval in outline, with
one side convex, the other almost flat. Each contains within it
endosperm and an embryo which lies curled up inside in the
form seen in i, Fig. 6. When germination commences, the
curved part (c) imbedded in the middle of the endosperm grows
and forces the end (a) of the embryo out of the seed. From
this exposed end, which is the radicle, a straight, slender, primary
root develops, the extent of which is seen at 3 and 5, Fig. 6.
The part of the young seedling which extends from the root
into the interior of the seed, grows very rapidly at first, at
the same time assuming a sharply bent outline (2, Fig. 6). It
comes above ground in the form of a close loop (c), but on further
growth the end within the seed is pulled out of the soil, and
grows up in the air. The tip within the seed changes and
absorbs the endosperm, and usually remains there until all the
nutrient material has been transferred from it to the various
centres of growth in the young plant. After the food-reserve
is exhausted the tip withers and becomes free from the seed-coat.
In loose soils the latter is pulled above ground before the endo-
sperm is exhausted, and remains on the end of the tip for some
time. In other cases where the soil is damper and of a stiffer
nature the seed-coat remains below ground altogether.
The curved part of the embryo which comes above ground
is a leaf. It is the cotyledon of the embryo, and is in reality a
thin hollow leaf like those of the full grown onion plant : within
it is the plumule, which consists of a series of hollow conical
20 SEEDS I STRUCTURE AND GERMINATION
leaves arranged one inside the other. Just at the point where
the root joins the cotyledon there is a thickening which marks
,C
FIG 6 x. Section of an Onion seed, a, Germination of same.
3 . Young seedling. 4 and 5. Same as 3, but some days
older. In 3 and 5 a secondary root is seen. > ^
a Radicle and primary root ; c cotyledon ; * slit in cotyledon
from which the first foliage-leaf of the seedling emerges ; J
endosperm of seed ; ground line.
the place where the plumule is situated within, and at a short
ONION
21
distance above this is a very narrow slit (s), through which the
first green leaf of the plumule makes its exit (j, 5, Fig. 6).
After one leaf emerges others soon follow, the younger ones
coming out in regular order through slits in the sides of those
immediately older than themselves.
Ex. 12. Soak fresh onion seeds in water for a few hours. With a razor
cut through some parallel to their flat sides in order to show the embryo
within, as at I, Fig. 6.
Sow others in damp blotting-paper; allow them to germinate and the
seedlings to develop ; make observations of them at different stages of growth.
Watch the germination of seeds sown in boxes or pots containing ordinary
garden soil.
FIG. 7. i. Outline of wheat grain showing the position and form of the
embryo. *. Longitudinal section through a wheat grain. 3. Wheat
grain germinating.
Sc Scutellum ; / plumule ; r 1 primary root ; r* one of the first pair of
secondary roots ; ce coloorhiza ; e endosperm.
13. Plants whose embryos possess only one cotyledon are
known as Monocotyledons, and form the second large class of
seed-bearing plants.
Few of the representatives of this class with which we are
ordinarily familiar have true seeds large enough for examination.
The onion is probably one of the best commonly occurring
22 SEEDS I STRUCTURE AND GERMINATION
examples which may be considered typical of the monocotyledons
and easily obtainable.
To this class, however, belong all the grasses, but their seeds
and embryos are so different in many respects from those of the
onion that it is necessary to examine one of them in detail.
Wheat. A wheat grain, which may be taken as an example,
is not a seed, but a kind of nut with a single seed within it.
The seed grows in such a way as to completely fill up the in-
terior of the nut, and become practically united with its inside
wall. The embryo occupies only a
small part of the grain, the rest being
taken up by the floury endosperm of
the seed (e 2, Fig. 7).
The embryo is easily seen at the
base of a soaked grain on the side
opposite the furrow. When removed
it has the appearance seen at i, Fig. 7.
The part of it which lies close up
to the endosperm is a flattened
somewhat fleshy shield-shaped struc-
ture called the scutcllum (sc)\ attached
to the front of the scutellum is the
plumule (/), consisting of a bud
formed of an extremely short stem,
upon which are sheath -like leaves
enclosing each other. The embryo
generally possesses five roots, one
primary and two pairs of secondary
FIG. s. i. Seedling wheat plant, rootlets ; the former and one pair of the
latter are seen in Fig. 7. They are all
& completely enclosed by a sheath which
j s con ti nuous w j t h the scutellum, and
are consequently not visible from outside ; their position, how-
ever, is marked by projecting bosses. The sheath round the
WHEAT 23
roots is termed the coleorhiza (GO 2 and 3, Fig. 7), and when germi-
nation takes place it expands and bursts the coats of the grain, the
roots about the same time breaking through the enclosing coleo-
rhiza. When a wheat grain is sown in the ground it remains there,
but the plumule grows upwards, its first leaf, the coleoptile, ap-
pearing above the soil as a single pale tube-like structure ; from
a slit in the tip of the latter the first flat green blade soon appears
(/, Fig. 8), and is followed by a succession of single green leaves, the
younger ones growing from within the older ones in regular order.
Ex. 13. Soak some white wheat grains in water until well swollen out,
and note the following points : The furrow along the back of the grain, the
bearded tip, and the side opposite the furrow. Keep them damp a day.
The embryo, which is easily seen through the semi-transparent coat, can be
removed by slitting round the circular cotyledon with a needle. Examine its
structure, and compare with Fig. 6.
With a sharp knife or razor cut through from back to front, so as to
divide the grain into two longitudinal halves, and note the floury endosperm
and the shape and parts of the divided embryo.
Place a folded sheet of damp blotting paper on a plate, sow some soaked
wheat grains on it, and cover with a tumbler. The grains will germinate.
Watch their development up to the time the first green leaf appears, taking
out the embryo and examining it at different stages of its growth.
There is difference of opinion as to which part of the embryo
is to be considered the cotyledon. Soine authorities regard the
scutellum as the cotyledon, while others give this name to the
coleoptile or first sheathing leaf which comes above ground, and
which has no green blade (/>, Fig. 8). Others, again, consider
that the first sheathing leaf is an extension of the scutellum, and
the two combined is therefore the cotyledon. In any case, there
is only one cotyledon present, and wheat therefore belongs to the
class of monocotyledonous plants.
14. During the growth of the embryo of a wheat grain, it will
be noticed that the endosperm becomes soft and decreases in
quantity as the roots and plumule expand and develop ; the
endosperm is the food upon which the young plant depends
during the early staggs of its life, the scutellum acting as a
34 SEEDS: STRUCTURE AND GERMINATION
structure for changing, absorbing, and transferring this reserve-
food to the growing parts which need it
Br. 14. Note the softening of the endosperm in germinated wheat grains
and its decreased amount after seedlings have grown considerably.
Remove the embryos from well-soaked grains, and grow them without
the endosperm on damp blotting-paper. Allow ordinary uninjured grains to
grow with them. Both the embryos in the grains and those removed from
the grains develop, but there is a great difference in the results after a few
days.
15. The store of reserve-food on which the young plant
depends for its early development is sufficient to enable it
to form a root, stem, and several leaves, as is evident when
seeds are allowed to germinate upon damp flannel or blotting-
paper, from which nothing but water is absorbed.
No food-materials or manures are needed for this primary
development, and seeds germinate and the seedlings grow for
a considerable time as well in poor soil or sand as in good
rich ground. As soon as the reserve store is exhausted hunger
becomes apparent, and unless the plants are then supplied with
suitable nutriment from the soil and air, and are also placed
under conditions favourable for growth, weakness and death
are likely to occur.
Among the larger seeds, such as beans and peas, where there
is an abundant store of reserve-food, the young seedlings begin to
manufacture food for themselves from materials absorbed from
the soil and air, long before their reserve is exhausted. In
small seeds the reserve is sometimes almost consumed before
the roots and leaves are sufficiently developed to carry on
their work properly, in which cases a more or less temporary
starvation and check to growth ensues. Especially does this
happen when seeds are sown too deeply, for a large amount
of food is then used in the production of a stem long enough
to lift the leaves up into the air.
CHAPTER III.
THE ROOT.
i. From observations made upon the seedlings mentioned in
the preceding chapter, it is seen that each of them is made up of
distinct parts, namely, root, stem, and leaves. These parts are
usually present in all the common flowering plants, and it is
needful to examine them separately and in detail.
Primary and Secondary Boots. It was noticed, when deal-
ing with the bean seedling, that its two ends always grow in
opposite directions ; the plantlet can be considered as an elon-
gated axis, one end of which bears the leaves and invariably
comes above ground, while the opposite end never bears leaves,
and persistently follows the plumb-line downwards. The de-
scending part is known as the root. As will be pointed out
later, all roots do not behave in this manner, and it is to be
specially noted that many of the underground parts of plants
are not roots ; the exceptions, however, may be left for future
consideration.
The first or primary root which the bean plant possesses is
merely an extension of the radicle of the embryo which exists
nrithin the seed. Soon after making its exit from the seed, it
takes a downward course, and elongates by growth taking place
near its tip.
Ex. 15. Germinate a broad bean on damp flannel. When the primary root
is about j of an inch long, make small dots upon it about A of an inch apart,
with a pen or fine brush dipped in Indian ink. Wrap the bean in damp cotton
wool, allowing the marked root to be free, and place it in the bottom of a
glass funnel with a narrow stem, so that the marked root projects down the
latter Cover over the ninvel with a piece of glass or cardboard to prevent
26
THE ROOT
evaporation, and, after allowing it to grow in a dark place two or tnree days,
take it out and notice the position of the dots on the elongated root. Measure
the distances apart, and find out which part of the root has grown most.
After it has grown two or three inches long, branches arise
upon it similar in appearance to the primary root itself, only
thinner (Fig. 9). Instead of grow-
ing vertically downwards, they grow
away from the primary root almost
at right angles to it. These lateral
branches lengthen in the same man-
ner by growth near their tips, and
are called secondary roots. They
ultimately produce tertiary roots,
which grow out obliquely from the
secondary ones, and further branch-
ing may go on in this manner until
a very extensive collection of roots
is obtained, the whole of which is
called the root-system of the plant.
2. On careful examination of a
well-developed root of a seedling
bean, the secondary roots are seen
arranged in five rows along the
primary root, and not in irregular order, as appears at first sight.
They are not, however, equi-distant from each other in the rows.
The first to appear arise near the cotyledons, followed subse-
quently by others, which grow out at points nearer the tip, the
youngest being always nearest the apex of the primary root,
the older ones farther away from it. The relative age of the
various lateral roots can therefore be determined by examina-
tion of their position on the primary root. This kind of
sequence where the youngest parts are nearest the tip of the
axis on which they grow, and the older ones farther away from
rt in regular order, is known as acropetal^uccession.
FlG. 9.^, Primary root of bean,
showing lateral secondary roots ; h
root hairs. B, Longitudinal section
of a similar root, illustrating the en-
dogenous origin of the 'lateral roots.
PRIMARY AND SECONDARY ROOTS 27
3. Another point to be noted is that the lateral roots do not
arise as up-growths on the surface of the primary root, but come
from within it, and are described as endogenous. The slits which
they make in the substance of the primary root, and through
which they emerge, can be readily seen in a bean seedling
(A, Fig. 9, a). A section of a root lengthwise, as at 2?, shows
that the secondary lateral roots are connected with its central
more solid core ; the three lowest ones, although they have just
begun to grow, have not yet penetrated the outer layer of the
root, and would not be visible on the outside of the latter.
This mode of origin is characteristic of lateral roots generally
wherever they are met with.
Ex. 16. Germinate and allow broad beans to grow upon damp flannel as
in Ex. 3. Watch the development of secondary roots, noting their position
and longitudinal rows on the primary root. Slice some and note the endo-
genous origin of the secondary roots.
Very carefully dig up a half-grown mangel, turnip, and carrot ; wash away
the soil and note the arrangement of the secondary roots on the primary root.
Make a deep longitudinal slit with a knife through the ' rind ' down to the
1 core ' of a carrot. Split off the ' rind ' and examine the ' core ' from whence
the secondary roots arise. How many rows of the latter are there ?
4. Many dicotyledonous plants have roots similar to those of
the bean plant. When, as in this case, the primary one continues
to grow, keeping distinctly larger than the lateral ones, it is called
a tap root. Very good examples are met with among cultivated
plants in the carrot, mangel, red clover, and mustard j in shep-
herd's-purse, poppy, and many other weeds, as well as in most
broad-leaved trees.
A number of plants have swollen fleshy roots in which food
materials are stored for future use ; they are described as tuberous
roots, and must be distinguished from tubers, which are fleshy
underground stems.
To designate the different forms of thickened roots various
special terms are in use. The typical carrot root is conical] that
28
THE ROOT
of the turnip napiform. The root of the radish is spoken of as
fusiform.
In some instances the primary root is soon rivalled in size by
its branches ; it may even cease growth altogether. Such plants,
on being pulled out of the ground, exhibit a bunch of slender
roots, the chief of which are all much the same diameter and
length ; roots of this character are described as fibrous^ and are
well exemplified in common groundsel and grasses.
5. Adventitious Roots. The roots of monocotyledonous
plants differ in their development from those of dicoty-
ledons. The single primary root of
the onion, for example, lasts but a
short time, and is succeeded by others
which do not arise as branches upon
the primary one, but spring from the
very short stem of the plant. Roots
which arise on stems and leaves, or on
various parts of the roots of plants,
but not in acropetal succession are
described as adventitious. They are
very common upon all monocoty-
ledonous plants of the farm and garden,
and may be considered the chief
ones which such plants possess. In
wheat, for example, the embryo within
the grain possesses three roots; in
barley, five or six. These are, how-
ever, merely temporary structures of
FIG. 10.- Young barley plant show- use during the earlier stages of growth.
ing adventitious roots (a) grow- ^ ^ ,, , i_ i i
ing out from the first jomt or By the time the wheat or barley plant
nodeof the stem.
ground the primary roots of the embryo are succeeded by
adventitious roots which grow out from the lower nodes or joints
of the stem near the surface of the soil (Fig. 10).
ADVENTITIOUS ROOTS 29
Although common upon monocotyledons adventitious roots
are not confined to this class. Examples are abundant upon
many kinds of dicotyledonous plants. Good instances are met
with on the underground stems of mint, potato (Fig. 144) and
hop, and on the runners of the strawberry, stems of creeping
crowfoot (Fig. 21) and white clover, as well as many others.
They are generally produced at the joints where leaves grow
upon the stem, and may arise in some plants (e.g., on strawberry
runners) from internal causes apart from any external influences ;
in other instances their development depends upon contact of the
stem with water or moist soil. Almost all parts of certain plants
may be made to produce them, and the propagation of plants
Buch as gooseberries, currants, roses and hops by means of slips
and cuttings depends upon their development. Pieces of stem
cut off just below a leaf, and placed in moist earth soon develop
adventitious roots near the cut end. Advantage is taken of their
formation in the propagation of plants by means of layers.
Ex. 17. Examine the roots on young strawberry runners in July. Also
those on creeping crowfoot, young shoots of ivy, underground stems of
potato, couch-grass and mint, and on the lower parts of the stems close
to the ground, of oats, wheat, and barley. Note the position, number, and
extent of these roots.
Examine the roots upon any cuttings or slips which can be obtained, and
observe whether they arise on the cut surface or at a point some distance
away from it.
Usually adventitious roots are thin and fibrous, but those of
the dahlia are tuberous.
6. The complete root-systems of plants vary enormously in
extent, but in all cases the total length is much greater than is
usually anticipated. That of an ordinary oat plant, although not
spreading through more than a cubic yard or two of soil,
measured in one instance over one hundred and fifty yards in
length.
A tree uprooted by the wind exposes to view a small number of
30 THE ROOT
stout roots similar to the thicker branches of the crown, and from
these are given off a larger number of a finer texture. By far
the greater bulk, however, which the tree possessed remain in the
ground in the form of extremely fine rootlets or fibrils extending
outwards generally as far, or a little farther, than the branches
and leaves of the tree, but in some instances to much greater
distances. Not only do the roots grow out horizontally and near
the surface of the soil, but they extend downwards as well. In
isolated instances, where an adequate supply of air has been
maintained along open cracks and fissures, roots have been
found to descend many yards into the ground, but in general
the roots of the tallest trees rarely go down more than seven
or eight feet The want of air and presence of noxious sub-
stances in the lower regions of the soil checks further growth in
this direction.
With many plants almost every cubic inch of soil immedi-
ately beneath their shade contains fine delicate rootlets, and the
extent of their root-branching is very rarely realised on account
of the ease with which these hair-like fibrils are broken off when
the plant is pulled up or disturbed.
Many forest trees have a natural habit of sending their roots
several feet into the soil Examples of fruit-trees belonging to
this class, and requiring a deep soil for proper growth, are the
cherry and wild pear.
Some trees, such as larch, keep their root-system nearer
the surface, spreading out more horizontally in the ground.
The quince, used as a stock on which to graft pears, has roots
which remain in the upper regions of the soil. Similar surface-
rooting habit is very marked in the * Paradise J apple on which
apples are grafted, and in Prunus Mahaleb upon which cherries
are often grafted.
The root-system of wheat penetrates more deeply than that
of barley ; the mangel sends its fine rootlets more extensively
into the deeper layers of the soil than cabbage or turnip;
EXTENT OF ROOtS 31
red clover roots more deeply than white clover, and almost all
plants have distinct and peculiar habits in this respect
7. The character and extent of root-development is not, how-
ever, altogether dependent upon the species of the plant con-
cerned, but is materially influenced by external circumstances,
such as the texture of the soil, and the amount of water in it.
In deep open soils and loose sands the root-system of a plant
is much larger than that of a similar plant grown in compact
heavy ground.
In soils which are not water-logged, increase of moisture up
to a certain extent increases the branching of the root, and
excellent examples of the influence of water, coupled with good
air supply, are seen in well managed plants in pots, and also
among plants growing near wells and in drain pipes ; the latter
in some instances become completely blocked by the large
number of fine rootlets of trees growing in their neighbourhood.
The root-system is also considerably modified by the totyl
amount and kind of the manures or food-materials present
in the soil. Up to a certain point an increase of nutrient
substances increases root-development; an excess hinders it.
Mutilation influences the development of the root-system. If
the growing-point of the tap root of a cabbage or tree is cut off
its further elongation is prevented, but the secondary roots make
up for the loss by more vigorous growth and often many adven-
titious roots arise near the cut end.
In order to properly cultivate plants of all kinds it is very
important to study the habit or manner of branching of their
roots and the relative proportions of the thick tap and second-
ary roots to the fine ramifications to which they give rise and
which spread through the soil in all directions. The proportion
of root-system below ground to the branches and leaves above is
also worthy of attention.
The adaptability of plants to the various kinds of soils, their
need of water, the cultivation which the ground should have and
32 THE ROOT
the rational application of manures to the plant are best under-
stood and appreciated after a careful study of these points. Tap-
rooted crops, such as sugar-beet, mangel, carrot, and parsnip,
require the soil to be well-worked to some considerable depth.
Surface-rooting plants, such as barley, can be grown upon
comparatively thin soils. The same is true of pears grafted on
the quince and apples on the Paradise stock, and such plants
respond more quickly to, and are more benefited by, top-dressings
of soluble manures than plants with a deeply-penetrating root-
system.
Ex. 18. The student should dig up and examine specimens of the roots
of all the chief plants of the farm ; especially is it necessary to investigate
the general form and extent of the roots of the common weeds of arable
and pasture land. Begin with the examination of young seedlings, which are
readily obtained in a complete condition. Note the presence or absence of
tap root, extent of branching, the depth to which they descend, and their
horizontal extension.
8. Boot- Hairs. On the root of a seedling bean grown on damp
flannel or blotting-paper is seen a fine white silky band of hairs.
These are called root-hairs, and they are never present at the
extreme tip of the root but arise at some distance behind its
growing point. As the root elongates the root-hairs on the
older parts die and turn brown, but others are produced on
the younger parts, so that no matter what the length or size of
the root may be for a short distance behind its tip it is clad
with these delicate transparent hairs. When secondary roots make
their appearance hairs are produced upon them in the same
manner and follow the same order of development as those upon
the primary root.
Their size and abundance are dependent on the species of the
plant, and the amount of moisture surrounding the root. Plants
growing in very wet situations or completely in water have
few or no root-hairs. In very dry soils their development is
checked, the greatest abundance being met with in moderately
damp soils.
ROOT-HAIRS 33
A good supply of lime is found to increase the number and
length of the root-hairs of many plants.
The hairs are hollow tube-like structures and should not be
confused with fine small rootlets. They are outgrowths from
the surface of the root (Figs. 72 and 78), and as long as they
last are concerned with the absorption of water and various in-
gredients in solution from the soil.
Upon plants growing in the ground the root-hairs are very
intimately in contact with the particles of soil and are of so
delicate a nature that it is practically impossible to remove a
plant without destroying them.
Ex. 19. Germinate beans, mustard, oats, barley, and wheat in damp
flannel, and examine the root -hairs on the primary roots. Note their delicate
nature, and their position, length, and abundance.
Although almost invisible they are among the most important
organs which plants possess. All the food constituents obtained
from the soil and from the various manures applied to the latter
are taken in by the root-hairs. By their means plants are kept
constantly supplied with water ; their destruction in the process
of transplanting or any disturbance of their development and
action, such as may be caused by excessive dryness or imperfect
aeration of the soil, leads to a deficient water supply and con-
sequent withering of the plant
CHAPTER IV.
THE VEGETATIVE SHOOT : STEMS, LEAVES,
AND BUDS.
i. IT has been already noticed that the seedling bean plant consists
of a descending portion, the root, and an ascending part which
comes above ground. The latter is known as the primary shoot,
and consists of an axis the stem upon which are arranged a
series of lateral appendages which are called leaves. The points
on the stem to which the leaves are attached are usually slightly
thickened, and are called nodes or 'joints/ the lengths of stem
between them being termed internodes. Flowers ultimately
arise upon the shoot, and it is one of the characteristics of seed-
bearing plants that seeds are always produced on their shoots and
never on roots. For the present, however, flowers may be left for
future consideration, and attention paid to the origin and nature
of the vegetative shoot or stem with its ordinary green leaves.
a. In the earliest stages of the development of a bean plant the
primary shoot is very short and bears the cotyledons or primary
leaves, its tip ending in the plumule.
The latter is a bud, and at the time when the seed commences
to germinate, its parts cannot be fully made out by observations
with the naked eye. As soon as it comes above ground, however,
the bud is found, on examination, to consist of a short stem
hidden by a number of enfolding leaves. An external view of it
in this stage is given at i, and a longitudinal section at 2, Fig. n.
As growth proceeds, the short stem inside the bud elongates,
and the leaves, which at first are crowded upon it, become
STEMS, LEAVES, AND BUDS
35
separated from each other. Marks
made upon the stem as previously
explained for the root in Ex. 15,
reveal the fact that the increase in
length takes place at the tip of
the shoot. After reaching a certain
length the lowest intervals between
the leaves cease to elongate; the
upper, younger and shorter ones
also lengthen and cease
in a similar manner, to
be followed in turn by
still younger parts of the
stem nearer the tip. The
stem, before the growing
season is over, may thus
reach a height of two or
three feet, or even more,
the extreme tip, or grow-
ing-point as it is called,
remaining young all the
time, and acting as a
manufactory for the ad-
dition of more stem and
leaves. The growing-
point, which is of a
tender and delicate
nature, is protected by
the enfolding young
leaves, the latter aris-
ing as outgrowths from
its external surface. The
youngest leaves are al-
ways nearest the tip of
FIG. ii.
x. Epicotyl of bean, with plumule.
2. Longitudinal section of the same ; ep epicotyl ;
/ terminal growing point of the plumule ; a a
leaf in whose axil is a bud b' ; b buds in axils of
inner leaves of the plumule.
3. Epicotyl, with plumule unfolding.
4. Later stage of growth of 3, showing connection
with bean seed ; ep epicotyl ; a first leaf
(rudimentary), in whose axil is bud V ; /"second
leaf (rudimentary) ; c and e ordinary foliage
leaves ; g buds in axils of the cotyledons ready
to develop into stems which may come above
ground.
36 THE VEGETATIVE SHOOT
the stem which bears them, the older ones being further removed
from it in regular order that is, they arise in acropetal suc-
cession, and adventitious leaves are never met with.
Ex. 20. I. Sow beans in pots or boxes containing a mixture of damp sand
and garden soil.
Cut longitudinal sections, and examine the structure of the stem and terminal
bud of a seedling as soon a* it has come above the surface of the soil.
2. Watch the development of the stem up to the time of unfolding of
the green leaves.
Observe the rudimentary character of the first leaves.
3. Make small marks on the stem about a quarter of an inch apart with
Indian ink, and observe which part elongates most.
4. Make similar observations upon the seedlings of mustard and peas.
3. While numerous annuals, such as mustard and charlock, and
some perennials, resemble the bean, many plants differ somewhat
from it in the development of the plumule. Instead of the latter
growing at once into a long shoot, bearing leaves at some dis-
tance from each other, the primary axis within the plumule
elongates very little, its internodes remain very short, and the
leaves arising upon it appear crowded together, usually in the
form of a rosette, a short distance above where the cotyledons
were placed ; this form of stem with short contracted inter-
nodes is well illustrated in the first season's growth of mangels,
turnips, carrots, certain thistles, and red clover. In such plants
as these, the primary root and hypocotyl become much thickened
by the deposition within them of reserve-food prepared by the
leaves, and it is only during the following year that the
growing-point of the stem, which is hidden in the centre of the
rosette, elongates and produces a shoot with long internodes,
and bearing a series of new leaves at considerable intervals.
In the onion and many bulbous plants the primary stem also
remains very short, and the reserve-foods prepared by them
are deposited in the bases of the leaves, instead of being
stored in the root and stem, as in the former instances (see
Fig. 24).
BUDS
37
4. Buds. The stems and leaves of all flowering plants originate
from buds in the manner indicated above ; buds may therefore be
termed embryonic or incipient shoots. It is by their growth that
trees, which appear so bare in winter, become clothed with fresh
green leaves in the succeeding spring. The relationship which
they bear to the leaves and stems produced by them is easily
discerned by examining the structure and watching the develop-
ment of the terminal bud of a young sycamore tree (Fig. 16).
On the outside is observed a series of scaly leaves, which
overlap each other,
and protect and cover
up the delicate grow-
ing point of the twig.
A section through the
bud (Fig. 12) shows
the disposition of
these scaly leaves
and within are also
seen the ordinary
leaves (/) arranged
upon a very short
stem (s). In spring
the inner scaly leaves
grow for a time (a,
Fig. 13), and
FIG. 12. Longitudinal sec-
i ilQn of a terminal bud of a syca-
Ultl- more tree as seen in autumn.
f 11 er i bud-scales; j rudimentary stem,
fall On, leaV- with foliage-leaves /; b lateral
FIG. 13. Terminal bud
of sycamore, similar to
that of Fig. 12, develop-
ing in spring, a. bud-
scales ; / foliage-leaves ;
b lateral bud.
ing small scars where u
they were attached to the twig. The stem (s\ which bears
the rudimentary green foliage-leaves (/), elongates, and the latter
are pushed out from between the protective scaly leaves of
the bud (Fig. 13). After a week or ten days, the stem has
reached a considerable length, and the leaves, which were rudi-
mentary and packed away in the bud, unfold themselves and
grow out flat as in Fig. 14.
38 THE VEGETATIVE SHOOT
The number of foliage-leaves present upon a developed shoot
is often indicated in the bud, but in some plants, especially those
of a herbaceous character, the growing point of the bud con-
tinues to produce new leaves until frost checks it in autumn.
Ex. 21. Cut longitudinal sections through a Brussels sprout and the ' heart '
of a cabbage. Note the stem, leaves, and axillary buds within.
Ex. 22. Examine with a lens longitudinal sections of the buds of sycamore,
horse-chestnut, oak, beech, and other trees.
FIG. 14. Later stage of development of bud in Fig. 13. a Bud-scales falling off;
j stem ; / foliage-leaves in axils of which are lateral buds h.
5. The vegetative shoots of plants usually end in
terminal buds> and an examination of almost any kind of
plant shows that not only are buds present at the tips of the
stems, but on their sides as well. These lateral buds arise
ordinarily in the upper angles formed where the leaf-bases and
stem join each other. The angles are termed the axils of the
leases, and the buds are designated axillary buds. Most fre-
BUDS 39
quently only one bud is produced in each leaf-axil, but in some
instances, two or more may be present.
6. Generally the first leaves of the bud which are outermost
or lowest down on the stem, are rudimentary structures, smaller
and different in appearance from those which unfold later. In
the primary bud or plumule of the bean (Fig. n), and many
similar herbaceous plants, this is observable, but it is most
evident in buds which are met with upon perennials, such as
shrubs and trees. In the latter the outermost leaves of the buds
are generally more or less firm, tough structures, termed scales or
scale-leaves, which protect the interior of the bud from being in-
jured by frost, rain, and other agents during the winter. Buds,
such as those of the sycamore (Fig. 16) and pear (Fig. 17),
having scales are termed scaly buds, those without, such as mealy
guelder-rose, being known as naked buds.
7. Buds similar to those of the bean and sycamore, previously
described, which develop into shoots bearing green foliage-
leaves, are termed leaf -buds : when met with upon trees they are
sometimes named wood-buds, as it is from them that new woody
twigs are produced. Many buds, however, on opening, give rise
to flowers only, and are termed flower-buds : a third kind is met
with producing short shoots bearing both green leaves and
flowers; these are mixed-buds. Among gardeners the two
latter forms are known as fruit-buds, as it is from them that
fruit is obtained. The general appearance and development
of a mixed bud from a pear tree is illustrated in Figs. 17
and 1 8.
It is not possible in all cases to distinguish fruit-buds and
wood-buds by their outward appearance, although for budding and
pruning operations and the general management of fruit-trees it
is desirable to do so. In apples and pears the wood-buds are
small and pointed, the fruit-buds being blunter, more plump,
and of larger size. In cherries and plums both kinds are very
similar in appearance ifc winter, and it is only in spring when
40 THE VEGETATIVE SHOOT
they begin to develop that the stouter and blunter characters of
the fruit-buds show themselves.
Their position upon the shoots is a great aid in distinguishing
the two classes of buds (see pp. 44-50).
8. Branching of Stems. The axis or stem of the primary
shoot of plant is at first single, and may continue to grow
as a simple straight structure. Usually, however, after a time,
branches or secondary axes arise upon it, and these in all cases
proceed from buds. In Fig. n, of the primary bud of a bean,
secondary lateral buds are seen in the axils of the leaves of &
and If : these are flower-buds, and consequently do not produce
long leafy shoots ; but secondary axes bearing green leaves fre-
quently occur in the bean, and are generally produced from
buds in the axils of the cotyledons as at g (Fig. n).
In many plants the buds in the axils of each leaf of the
primary stem develop into leafy shoots, and upon the latter
branches may again arise in a similar manner. The total
number of stems bearing leaves may thus become very large
on a single plant. In the best fodder crops, where large yield
is always a desirable feature, branching is exhibited in high
degree, and the same may be observed in trees of all kinds,
and many weeds, such as groundsel and chickweed.
9. The main stem of a plant is spoken of as a primary axis, or
axis of the first order, the branches upon it being secondary axes,
or axes of the second order, those borne by the latter tertiary
axes, and so on. For purposes of convenience in description,
any axis may be considered a main one, its branches then
being secondary axes.
10. When a stem continues to grow at its apex, for a long
time it is spoken of as indefinite in growth : the branches upon
it are usually many in number, and smaller than the main stem.
This form of branching is spoken of as racemose (a, Fig. 15).
In many plants the terminal bud produces a flower or a
collection of flowers, and the main axis ''.hen ceases to elongate ;
BRANCHING OF STEMS 41
such a stem is definite in growth. When lateral branches arise
upon it, they are generally few in number, and soon equal or
exceed the main stem in vigour. Branching of stems of definite
growth is said to be cymose \ it often resembles the diagrammatic
sketch , Fig. 15. Cymose branching, however, sometimes
leads to the formation of what at first sight appears to be a
simple main axis of indefinite growth, but which is in reality
composed of a series of short axes of different orders. At
r, Fig. 15 is a main or primary axis i, which ends at x, its
growing point having developed a flower or been destroyed
by frost, wind, insect attacks or other means, and elongation
FIG. 15. Diagrams illustrating (a) indefinite growth of stem,
and racemose branching ; (&) and (c) definite growth of stem and *
cymose branching, x, 2, 3, axes of first, second, and third order
respectively.
thereby prevented. Below its tips a lateral bud has pro-
duced the branch or secondary axis 2 : the latter axis soon
ceased growth, and a branch of the third order, 3, was pro-
duced, a further one, 4, being developed in a similar manner.
The whole shoot from A to J?, although crooked at first, may
ultimately straighten and appear similar to a simple single axis
of the first order of indefinite growth : when this happens such
a stem is termed a false main-axis or symfodium.
The branches of elm, hazel, and many other trees which
THE VEGETATIVE SHOOT
appear straight and of indefinite growth, are often in reality
sympodia, the terminal bud upon each annual shoot having
been destroyed or terminated by a flower, and a false axis
formed by the subsequent
vigorous growth of the
highest lateral bud. The
' spurs ' or short shoots on
pear (Fig. 17), apple (4,
Fig. 19), and currant trees
and also many of the under-
ground shoots of grasses
are examples of sympodia.
Ex. 23. Examine the kind of
branching of the shoots of vari-
ous common plants, such as
groundsel, chickweed, nettle,
charlock, mustard, vetches,
beans, peas. Note the origin
of the branches above the leaves.
ii. Twigs of Trees in
Winter. A study of the
appearance of the shoots
of trees in winter and their
subsequent development
during the following spring
and summer is instructive.
On the sycamore branch
shown in Fig. 16, large
terminal buds are visible
and several lateral ones,
FXG. 16. Piece of sycamore stem as seen in autumn. U pnfkqt U w hirh are well-
For explanation see text. DCneain WHICH are ^ Gil
marked leaf-scars, as at 2,
indicating the place where the leaves were attached in the previ-
ous summer. In 1896 the part marked c i897 did not exist, but
TWIGS OF TREES IN WINTER 43
the twig was terminated by a bud similar to that of Fig. 12, and
had also two small lateral buds resembling , Fig. 13. In
the spring of 1897 the buds opened, and the bud-scales fell
off and left scars at 4. The terminal bud then grew as in Figs.
13 and 14 and produced a considerable length of stem marked
1897, with several lateral buds upon it, each of which developed
in the axil of a leaf, as at h, Fig. 14. From the small lateral
buds just beneath the terminal one short shoots originated in
a similar manner.
12. The amount of growth of twigs during one year or one
growing-season is represented by the length between two sets of
bud-scale scars (4, Fig. 19, n l to 2 ).
As the scars are often visible upon the bark for several years
they are useful aids in the determination of the age of any length
of tree, stem, or twig. Frequently small buds are present in the
axils of bud-scales, and as the internodes between the latter
remain short such buds appear crowded together upon the twigs
and are often visible after the scars have been obliterated (Fig.
57, between A and -#).
The length of stem which a bud produces during a year's
growth is very varied, some leaf-buds giving rise to shoots not
more than a small fraction of an inch long, while others reach a
length of several feet. Much depends upon the kind of plant,
its age, treatment, and the position of the bud upon the tree, as
well as upon external circumstances, such as climate and soil
In trees which are unmolested the length of the shoots produced
each year by the terminal buds goes on increasing from extreme
youth onwards until a certain age is reached, after which the
yearly length of the shoots begins to diminish. The age at which
the growth is at a maximum is different for different trees, some
forming their longest shoots when they are 1 5 to 20 years old,
others not until 30 to 40 years have elapsed. In old age the large
number of buds to be supplied with water and food-constituents,
their increasing distance from the water-supply in the
44 THE VEGETATIVE SHOOT
ground, prevents the extensive growth which is noticed in youth :
the shoots upon aged trees are therefore very short.
The difference in the general appearance between young and
old trees is striking ; so long as long shoots are produced the
crown or head remains open and largely composed of long
straight branches, but when the formation of short shoots begins
the crown assumes a denser aspect.
In most trees the terminal bud of a shoot usually develops
the strongest shoot, the lateral buds giving rise to shorter
branches in regular decreasing order from the tip to the base,
where the buds usually produce very short shoots or none at
all. In the ash and willow, however, the branches on a shoot are
much the same size from top to bottom, and in a few instances
the branches are short near the tip and base and long near the
middle of the shoot In good soil and a favourable climate the
branches of trees are longer than where the ground is poor and
lacking in moisture or where the climate is severe.
Nitrogenous manures and absence of light due to overcrowding
tend to the production of long shoots, while the bearing of fruit
checks the vigour of trees and leads to the formation of short
shoots.
13. * Spurs/ The short branches upon trees often grow very
little each year and may take many years to reach a length of
even four or five inches. They are readily recognised by the
large number of ring-like scars which mark the place where the
bud- scales have fallen off each year. Upon fruit-trees they are
known as spurs or fruit-spurs^ and they need special attention,
as it is upon them that fruit buds are most frequently borne in
some kinds of trees.
The formation of a fruit-spur and its development is illustrated
in Figs. 17 and 18.
4, Fig. 19 is a typical piece of a long shoot of an apple tree
three years old bearing fruit-spurs.
The part 1898 is one season old, anti grew from a terminal
SPURS
45
bud arising at 2 , the bud-scale scars being visible at this point
The three buds upon it similar to a are wood-buds : they may
in 1899 develop into (i) long shoots, or (2) short ones, or (3)
remain undeveloped. The part of the shoot between the bud
scale-scars n l and 2 is the previous year's growth, namely, that
of the summer of 1897. The buds upon it in the winter of 1897
were similar to those marked a: during the summer of 1898,
when the terminal bud at n 2 was growing into a long leafy shoot,
they developed short leafy shoots, similar to B and C, Fig. 1 7, each
of which went to winter rest with a terminal fruit-bud upon it.
FIG. 17. A) Piece of last season's shoot of pear tree with wood or leaf-bud as seen in
autumn. J3, The same in the following midsummer ; the bud has now given rise to a short
shoot or ' spur' bearing leaves and terminated by a fruit-bud. C, The same as B after
leaves have fallen in autumn, showing 'spur* terminated by the plump fruit-bud.
Parts similar to , therefore, are not merely stalked buds, but
short branches bearing terminal fruit buds ; they are one-year-old
fruit-spurs, the terminal buds of which in 1899 will open into a
short stem bearing flowers similar to B y Fig. 18. At d is a bud
still in the undeveloped condition in which it was first produced,
and is therefore similar to a, except that it is two years old : it is
a dormant bud.
4 6
THE VEGETATIVE SHOOT
Upon the three-year-old piece of the shoot marked 1896 are
two spurs, c and *, two years 1 old. In 1897 they resembled b,
FIG. 18. Fruit-bud of pear (same as C of previous Fig.), showing various stages of its
growth. A, opening in spring ; B< later with flowers and leaves expanded ; (', later still,
only one flower has 'set or developed into a fruit, the re t having fallen off at b\ a t a
lateral bud which will continue the growth of the spur in the following year.
and in the spring of 1898 opened into a stem bearing flowers,
such as j, Fig. 18. Fruit was produced during the summer, and
SPURS
47
1838
1898
FIG. 19 Shoots of various fruit-trees.
x. Morello cherry. A to B, Ion* shoot of last sea on, 1898, with fr*it-buds t f\
nmiiar shoots of 1897 and earlier years are practically bare, w a spur.
a. Black currant. A to B, long shoot of last season, with frvit-b*ds t b ; long shoots
of previous year havefruibbiidt on spurs, *.
3. Plum. A to B) long shoot of last season, with wood-bud* t b\ long shoots of pre-
vious year have jrvit-buds on spurs, which terminate in a wood-oud, *, and bear
lateral fruit-buds, x.
4. Apple. * a to /", long shoot of last season, with vtood-buds, a \ long shoots of pre-
vious year have spurs which terminate in fruit-buds, b and o. For further ex-
planation Me text.
48 THE VEGETATIVE SHOOT
the large scar at x indicates that one apple ripened, the small
fruit-scar at x on spur e being evidence that the fruit fell from
the latter prematurely.
It must be noticed that after the production of fruit such a
spur as this cannot continue growth in the same line ; it may
die altogether, but usually one or more lateral wood-buds arise
upon it in the axils of its leaves, and these continue its future
growth. On spur c the lateral bud o has arisen in this manner
during 1898 when the fruit was being ripened. The spurs of
f
A B
FIG. 20. A , 4 Spur ' of pear tree which has borne one mature fruit at x ; a a fruit-bud.
B, An old 'spur' from the same tree; i, 2, and 3, growth of three suc-
cessive years, forming a sympodium : x large scars left where fruit has
matured and fallen off ;/ fruit-buds.
the apple and pear, therefore, present a zig-zag appearance (see
Fig. 20); those of black currant are* similar.
The spurs of the plum terminate in wood-buds, and con-
sequently grow in a straight line ; the lateral buds are fruit-buds
(3 Fi g- J 9)-
No hard and fast rule can be laid down in regard to the
position of the fruit-buds upon trees, as it is not absolutely
constant for any one kind ; exceptions occur due to manuring,
cultivation, season, kind of tree, and the pruning it has received.
SPURS 49
Three fairly distinct classes of trees may, however, be recog-
nised. Some trees, such as the peach, bear almost entirely on
long shoots one year old and have few or no spurs, while others
produce their fruit-buds chiefly at the apex or on the sides of
spurs, the long shoots of the tree bearing only wood-buds in
their first year ; a third group bears almost equally both upon
long shoots and spurs.
The apple and pear produce fruit-buds chiefly upon spurs,
and rarely upon long shoots which are only one season old. A
few varieties of apples, however, such as Cox's Orange pippin,
Ribston pippin, and Irish peach, sometimes produce fruit-buds
freely on the long shoots of last season.
The plum bears largely upon spurs (j, 3, Fig. 19), but sometimes
the fruit-buds may appear upon its young long shoots : when the
latter happens they are usually accompanied by wood-buds placed
on each side.
The red currant carries its fruit chiefly upon spurs ; the black
currant, both on young long shoots and spurs, but chiefly on the
former.
In the black and white Hearts, Bigarreau and Duke cherries,
the fruit-buds are mostly met with upon spurs, but the Morello and
Kentish types bear largely upon the one-year-old long shoots
(i, Fig. 19).
The gooseberry and apricot resemble the black currant in the
arrangement of their fruit-buds.
The raspberry bears upon leafy shoots, which arise in summer
from buds on the previous year's cane. The canes or stems
which come above ground are biennial. The fruiting cane dies
down in autumn, but before this takes place the buds at its base
on the underground rootstock grow up into canes : in the fol-
lowing year the buds upon the latter open out into leafy shoots
which bear the fruit, after which these canes die away, and are
followed by a new set of young canes which originate in a similar
manner.
5
SO THE VEGETATIVE SHOOT
There is considerable difference in the age to which fruit-spurs
attain ; some, like those of apple and pear, live many years ; upon
red currant they remain productive longer than upon the black
currant ; the spurs on the Morello cherry are shorter lived than
those upon the other varieties. In pruning those trees with
spurs of short life, endeavour should be made to secure relays of
young long shoots at frequent intervals.
14. Dormant Buds. On examining trees in spring when the
buds are beginning to develop, it will be observed that some of
them remain inactive and continue in this condition all the
summer. Not only may they refuse to grow in what may be
termed their proper season, but they frequently remain unde-
veloped for long periods. Such buds are termed dormant or
resting buds, and are met with upon almost all kinds of plants,
chiefly near the base of the stems, as at </, 4, Fig. 19.
Although many dormant buds soon die, some remain capable
of development for several years after their formation, and may
give rise to what are termed deferred shoots. In fruit-trees they
are termed c water-sprouts ' j if they spring from beneath the
surface of the ground they are known as ' suckers.' They not
uncommonly arise upon 'stocks' which have been grafted or
budded
Destruction of the terminal and lateral buds near the top
of a stem tends to promote the growth of deferred shoots from
dormant buds at its base. This is well illustrated in shoots of
fruit-trees and roses when they are pruned severely. Moreover,
pinching out the terminal buds of herbaceous and other plants
is often practised with a view to insure the development of all the
lateral buds upon it, and the formation of a bushy plant instead
of one with a single main stem and few branches.
The grazing and mowing of grasses promotes the full develop*
ment of all their buds, and a consequent increase of leafy
stems.
Not only does cutting away or pinching dff the terminal buds
ADVENTITIOUS BUDS 51
promote the development of basal buds likely to become dor-
mant, but anything which impedes the movement of water or
'flow of sap' to the terminal and highly-placed buds tends
towards the same result.
In the early formation of cordon fruit-trees, where it is important
that all the buds upon the main stem should develop shoots or
short spurs, bending the shoot for a time is practised in order to
promote the ' breaking ' of those buds at the base of the stem
which might otherwise remain dormant and leave a length of
unfruitful wood.
15. Adventitious Buds. Dormant buds, mentioned above, are
buds which have arisen in regular order in the axils of leaves, but
which have remained inactive some time ; the only irregularity
about them is their period of development. Buds may, however,
arise at any point of a plant, not necessarily in the axil of a leaf,
but on any part of the stem, or even upon roots and leaves : such
are termed adventitious buds. Examples are met with on the
roots of docks, poplars, roses, and many other plants, especially
when the upper bud-bearing parts have been removed. They
frequently arise and produce shoots upon stems which have been
injured. In some instances they proceed from the callus cover-
ing the wounds where branches have been cut off ; some of the
shoots of ' pollard ' trees spring from adventitious buds originat-
ing in this manner.
Adventitious buds are often produced upon leaves which have
been removed from the parent and pegged down on moist sand
or loam. Gardeners take advantage of this peculiarity in pro-
pagating begonias.
Similar buds occur upon some kinds of leaves when they are
severed from the plant and their petioles stuck in moist ground :
the scales of the hyacinth and other bulbs give rise to new
plants in this manner.
Ex. 34. Examine twigs of ash, sycamore, elder, horse-chestnut, oak,
beech, and other trees and shrubs in winter. Make notes of the arrange-
52 THE VEGETATIVE SHOOT
ment of the buds, the scars left where the foliage-leaves and old bud -seal ei
have fallen off, and the hairyness, smoothness, and any other peculiarities of
the bark and buds. (See Tables, page 6 1.)
Ex. 25. Measure the lengths of intcrnode between successive buds on last
year's shoots of the common trees and shrubs. At which parts, those which
are youngest or those which are oldest, are the buds most closely placed on
the stems?
Ex. 26. Examine young ash, sycamore, oak, and other trees in winter.
(1) Try and find out the yearly growth in length of the various parts of
each.
(2) Make observations in regard to the length of the branch produced by
buds near the apex, middle and base of each year's growth. Note the pre-
sence or absence of "dormant " buds.
(3) Find out if the branching is generally racemose or cymose. Look for
sympodia upon hazel, beech, elm, and horse-chestnut, and other trees.
(4) Note the difference in length of yearly growth of branches in very old
trees and young ones of the same species.
Ex. 27. Examine the long shoots and short shoots (' spurs ') of apple, pear,
plum, cherry, gooseberry and currant. Observe the size and form of the
buds upon the various parts of the shoots. Cut longitudinal sections and
examine with a lens : endeavour to determine which are wood-buds and which
are fruit-buds.
Ex. 28. Examine the unfolding buds upon the chief fruit trees in spring
when the different kinds of buds can be easily distinguished : observe the
position of the leaf-buds, mixed-buds, and flower buds respectively.
1 6. Stems and their Varieties. Stems which are soft and
which usually last but a short time, are termed herbaceous \
practically all our annuals have stems of this nature, and many
perennial plants also, e.g. nettles and hops. Most stems
which last several seasons develop within themselves consider-
able quantities of wood, and are harder and firmer in con-
sequence : such stems are said to be woody. It must be
pointed out, however, that herbaceous stems in reality also
possess wood, but only in the form of thin strands, which are
relatively small in amount when compared with the remaining
soft parts. All stems, moreover, are soft and herbaceous when
very young, so that no real distinction exists between herbaceous
STEMS AND THEIR VARIETIES 53
and woody stems, as it is a matter of degree of development
of the wood within them : a wall-flower or a rose, for example,
may be soft and herbaceous in its upper parts and hard and
woody below.
Trees and Shrubs have well-developed woody stems, the
former possessing a single main stem or trunk, which is devoid
of branches for some distance above the ground; the latter
have no very distinct main stem, and the chief branches are
all much the same in thickness and spring from a point either
on or close to the ground.
Many plants have stems which are too weak to maintain an
erect position ; they consequently grow along the surface of
the soil. Some plants have weak stems which always remain
prostrate^ while others, designated climbing plants^ have stems
which, although too weak to stand upright of themselves, are
nevertheless able to use suitable objects near them as supports.
Climbing plants support themselves in various ways. In ivy,
adventitious roots are developed on one side of the stem, and
these serve to fix the plant to bark of trees, walls, and rocks.
Tropaeolums of gardens and wild clematis are supported by
their leaves, the petioles of which curve round the stronger
branches of plants growing near them.
Peas and vetches are also enabled to climb by means of their
leaves, some of the leaflets of which are modified into thin thread-
like structures termed tendrils. The latter are sensitive to contact,
and wind round any slender object which they touch. Plants
such as the blackberry, rose, &c., are supported by means of
their stiff prickles.
In twining plants the whole stem upholds itself by twisting
round neighbouring objects. The stems of some of them
always twine to the right when growing round a support; the
hop is an example : others, such as bindweed, twine to the
left
17. A number of peculiar modifications of shoots are met with,
54 THE VEGETATIVE SHOOT
many of which receive special names; the most familiar are
mentioned below:
i. Above ground.
(a) In the wild pear, wild plum, hawthorn, sloe, and buckthorn,
some of the branches end in hard, sharp points, termed thorns
or spines. That they are modified shoots is seen from the fact
that they arise in the axils of leaves, and also themselves bear
leaves and lateral buds in some instances.
FIG. si. Runner of Creeping Crowfoot (Ranunculus refens L.).
r Adventitious roots; s intcrnodes.
(b) A runner or stolon is a shoot which extends horizontally over
the surface of the ground. Its internodes are long, and from its
nodes adventitious roots are produced, and grow into the soil
(Fig. 21). The buds present on the runner then become
fixed to the ground, and, developing into upright shoots, form
separate plants as soon as the internodes at s die away or are
severed.
Strawberry runners and those of creeping crowfoot are good
examples.
STEMS AND THEIR VARIETIES
55
Ex. 29. Examine the thorns upon the hawthorn, sloe, wild plum, wild pear,
and buckthorn. Note their origin in the axils of leaves, and that some of
them bear buds and leaves.
Ex. 30. Examine the origin of the runners upon strawberry plants, mouse-
ear hawkweed, and creeping crowfoot. Observe the position of the leaves
and buds upon the runners.
ii. Underground.
Stems within the soil sometimes resemble roots, but they can
be distinguished from the latter by the possession of leaves and
buds, and by their originating in the axils of leaves.
(a) A rhizome or ' rootstock ' is an underground shoot, which
grows more or less horizontally. Adventitious roots arise at the
nodes, and the internodes may be long or short, thick or thin, so
ViG.-22.-i. Diagram illustrating growth of an indefinite rhuome. A to B,
indefinite primary axis which remains below ground permanently, i, and 3,
lateral branches of A B which come above ground.
2. Diagram illustrating growth of a definite rhizome. A to /?, definite
primary axis which has flowered and decayed away ; a, a branch from the
primary axis coming above ground ; 3, a branch from 2 ; 4, a branch from 3.
The whole stem from A to C below ground is a sympodium or false main-axis.
that the general appearance of a rhizome is variable, those of
couch and other grasses being long, thin straggling shoots, while
in iris, hop and other plants they are thick and fleshy. When
leaves are present, they are generally reduced to the form of
membranous scales.
Rhizomes may be indefinite or definite in growth ; in the
former case, the true and main axis continues to grow at its
tip, and always remains below ground ; the parts which come
above ground are secondary or lateral branches, which arise in
the axils of its scaly l*aves (i, Fig. 22). Most rhizomes are, how-
56 THE VEGETATIVE SHOOT
ever, definite in growth, the main axis, after growing a longer or
shorter distance below, comes above ground, the continuation of
the rhizome within the soil being carried on by lateral branches
(2, Fig. 22). In perennial rhizomes of definite growth, such as
those of sedges, grasses, and many other plants, the permanent
part which remains below ground is a false main-axis or sym-
podium (p. 41).
(&) The term sucker is applied to any adventitious shoot which
originates below ground on the stems or roots of shrubs and
trees. It possesses adventitious roots and by separation from
the parent may become a new individual plant. Suckers often
develop very rapidly and rob the parent of water and nutriment,
so that except for purposes of propagation they should be
destroyed.
Ex. 81. Examine the underground parts of couch-grass, bindweed, mint,
potato, horse-radish, asparagus, raspberry, and hop, and observe the scale-
leaves and the buds in the axils of some of them.
Note the connection of the shoots which come above ground with the
underground parts.
(c) A tuber is a shoot with a short, thick, fleshy stem, and
minute scaly leaves, in whose axils are buds or 'eyes.' The
most common tubers are developed below ground e.g. those of
potato and Jerusalem artichoke but they may occur on parts
of plants above the soil. The scaly leaves are not visible on
the fully-developed potato tuber, as they drop off or shrivel
up before ripening is accomplished. For the development and
structure of the potato tuber see pp. 462-469.
(<t) A corm is a short, thick, fleshy stem, with a few thin, scaly
leaves covering it, and bearing one or more buds at its apex.
Examples are seen in the ordinary crocus and gladiolus of
gardens.
Fig. 23 is a section of a crocus in flower. At b is the solid,
fleshy stem of the corm, with the remains of an old corm (a) ad-
hering to it, and several adventitious roots (r). From its summit
STEMS AND THEIR VARIETIES
57
at h y the terminal bud has grown in spring into a short stem (<:),
bearing on its sides thin, membranous leaves (d) and ordinary
green foliage leaves (e\ which come above ground. One or
more flowers are produced
from the axils of the leaves, as
at / The substances stored
in the stem of the corm (b) are
used up in production of these
leaves and flowers, and conse-
quently, at the end of summer,
this part becomes shrivelled
and dead, like a. The green
leaves (e), however, after they
have developed, manufacture a
considerable amount of food, and
this descends from the leaves, and
is stored in the short stem (<:),
which thickens in consequence
and becomes a new corm at the
end of the season. The buds (x)
in the axils of the leaves of the
new corm remain near its apex,
carry on the production of a new
series of flowers, leaves and corms
in the following year.
A corm, instead of possessing
only one bud at its summit, as
at h, often has several buds there,
each of which develops into a
new corm in the manner de-
scribed; thus one corm may give rise to many in a single
season.
(e) A bulb often resembles a corm in external appearance, but
consists of a comparatively small stem, upon which is arranged a
FIG. 23. Section of Crocus in flower.
For explanation, see text.
THE VEGETATIVE SHOOT
number of thick, fleshy, scale-leaves, which overlap each other
more or less com-
pletely. The whole
structure is practi-
cally a huge bud,
and in the axils of
some of its scales
are small, rudimen-
tary buds. Familiar ex-
amples are met with
in the onion, tulip,
lily, hyacinth, snow-
drop, and narcissus.
The onion seedling,
figured on page 20,
develops several leaves
during summer, as
at A, Fig. 24, and
the plant swells at its
base and forms a bulb.
A section, as at ./?,
reveals its structure.
Tracing the leaves
from the green parts
downward, it is ob-
served that the bases,
especially of the inner
ones, are thickened,
and it is these leaf-
bases which form the
main mass of the bulb,
the stem (s) upon which
they grow being com-
pa*ratively small. At
B A
FIG. 24.^, Young onion plant ; a remains of an
old leaf; c c younger leaves.
B, LonRitudinafsection of the same ; j short stem ;
b leaves and leaf-bases forming the chief part of the
bulb ; / growing point of stem.
STEMS AND THEIR VARIETIES 59
the end of summer, the green parts of the leaves die and shrivel ;
their lower parts, which have become thin, act as a cover for the
rest of the bulb, and prevent the rapid loss of water from the
interior.
The onion bulb, if planted next year, forms adventitious roots
from the base of the stem, and the terminal growing-point (/)
inside grows up into the air, and produces leaves and an inflor-
escence of white flowers at the end of a long hollow stem. The
buds in the axils of the scale leaves develop usually in the same
manner, so that from one bulb several flowering shoots are often
produced. The materials stored in the bulb-scales are used up
in this development of the flowering stems, and after the pro-
duction of ripe seeds, the whole plant is generally exhausted,
and dies away, in which case the onion is a biennial plant.
Occasionally, however, some of the lateral buds from the axils of
the scales do not produce inflorescences, but leafy shoots only,
which form small bulbs in the same manner as an onion seedling.
After the death of the parent, these smaller bulbs remain, and
carry on the growth in the succeeding year. The onion plant
in this instance is a perennial.
A tulip bulb in autumn consists of a short, thick stem, upon
which are placed a series of large, overlapping, fleshy scales.
The latter are complete leaves, and not merely leaf bases, as
in the onion. At the apex of the stem is an embryonic shoot,
having leaves upon it, and bearing a terminal flower; in the
axils of some of the scales are rudimentary buds.
In spring the flower-bearing stem grows from within the bulb
and comes above ground, carrying with it the flower and two
or three leaves, as indicated in Fig. 25. This development
takes place at the expense of the food stored in the scales (o) :
the latter therefore soon become soft, and at the end of the
season shrivel up and decay. The leaves (e) on emerging
from the soil turn green, and during the spring and summer
manufacture a consfderable amount of food; that part of it
6o
THE VEGETATIVE SHOOT
not needed for the plant's immediate requirements is trans-
ferred to lateral axillary buds below ground, and is there stored.
These buds consequently grow rapidly and become young
daughter bulbs; one of them is
shown at n in course of development.
Bulbs like the onion, tulip, and
hyacinth, which have broad, concave
scales arranged in such a manner
that the outer ones completely en-
close those within, are known as
tunicated bulbs. In lilies the bulb
scales are not so broad, and are
arranged to overlap each other like
the tiles on a roof : such bulbs are
said to be imbricated.
Ex. 32. Cut a longitudinal section
through a young onion plant when the
bulb is well formed. Watch the develop-
ment of a young plant into an old bulb.
Cut sections of a mature onion bulb and
compare its internal structure with that of
a Brussels sprout.
Ex. 33. Examine old onion bulbs which
have been kept all winter and allowed to
sprout. Note the number of separate sets
of green leaves produced by it. Cut it
open and examine the origin of the latter.
Ex. 34. Cut longitudinal sections of
tulip, hyacinth, snowdrop, and narcissus
bulbs. Note the stem, the number of
scales, and their relative thickness in each ;
also the presence or absence of rudimentary
FIG. 25. Section of a tulip in
flower. / Stem on which are fleshy
bulb scales, o ; p flowering stem
bearing green leaves, e ; a ovary ; b flowers and axillary buds,
stamens ; c perianth of the flower ;
n bud developing into a new bulb ;
t small dormant buds.
Ex. 35. (i) Examine the structure of
a crocus corm in autumn. Pull off the outer
scaly leaves and observe the position and number of the buds on the thickened
stem. (2) Cut longitudinal sections of a corm. (3) Examine a corm in
bloom, and observe the roots, remains of old cormS, foliage and membranous
scale-leaves, and number and position of the flowers. Compare with Fig. 23.
BUDS OPPOSITE EACH OTHER 61
RECOGNITION OF TREES BY MEANS OF TWIGS
IN WINTER.
The chief deciduous British forest and fruit trees and shrubs
may be recognised in winter by the character and arrangement
of the buds, as given below :
GROUP I.
BUDS OPPOSITE EACH OTHER ON THE TWIGS (Fig. 26).
The following belong to this group :
Dogwood.
Mealy Guelder-Rose.
Common do.
Ash.
Spindle-Tree.
Privet.
Honeysuckle.
Elder.
Sycamore.
English Maple.
Norway do.
Horse-Chestnut.
Buckthorn.
1. Buds naked, i.e. without protecting bud-scales.
(a) Young twigs, smooth, slender, and blood-red in colour.
Dog- wood : Wild Cornel ( Cornus sanguined L. ).
(b) Twigs with a powdery grey covering consisting of stellate
hairs.
Mealy guelder-rose : Wayfaring-tree ( Viburnum
Lantana L, ). in s opposite ar-
2. Visible bud-SCaleS few (One Or tWO). rangementof buds.
(a) Bud-scales sooty black.
Ash (Fraxinus excelsior L.). Twigs smooth, greenish-grey ;
terminal bud much larger than the round lateral ones.
(b) Bud scales pinkish.
Common guelder-rose (Viburnum Opulus L.). Young twigs
with longitudinal ridges or angles, especially near their tips ;
lateral buds closely pressed to stem.
3. Several bud-scales visible ; closely and compactly arranged.
(a) Twigs slender, bright sage green.
Spindle-tree (Euonymus europaus L.). The bud-scales are
green, with pinkish margins and tips.
(b] Twigs slender; grey, brownish -grey, or brown; all buds small
and similar in size, including the terminal ones.
* Bud-scales smooth.
Buckthorn (Rhamnus catharticus L.). Many of the branches
62 THE VEGETATIVE SHOOT
terminate in a thorn : the buds of the shrub are not always
opposite; bud scales dark reddish-brown.
Privet (Ligustrum vulgare L.). Without thorns; buds much
smaller than the preceding, and their scales dark olive-brown ;
leaves often remain on all winter.
** Bud scales hairy, especially at the tips.
Common maple (Acer campcstre L.). The twigs are stiffer than
the two preceding shrubs; hairy when young Bolder parts of
bark with longitudinal cracks or fissures.
(t) Twigs stiffer and thicker ; terminal buds usually much larger than
the lateral ones.
Horse-chestnut (Atsculus Hippocastanum L.). Buds brown
in spring, covered with a sticky resinous substance ; large
triangular leaf-scar.
Sycamore (Acer Pseudo- plat anus L.). Bud-scales yellowish-green
with dark-brown margins and tips ; leaf-scar well marked.
Norway maple (Acer platanoidcs L.). Bud -scales pinkish or
reddish-brown, sometimes greenish at t.heir bases ; leaf-scar
narrower than in sycamore.
4. Several bud-scales visible, very loosely arranged.
Elder (Sambucus nigra L. ). Twigs pale brownish-grey, with longi-
tudinal ridges and distinct lenticels ; bud-scales brownish-red and
puckered ; very wide spongy pith.
Honeysuckle (Lonicera Periclymenum L.). The young twigs which
climb up and wind round supports are shining and cylindrical, with
a hollow pith. Bud-scales brownish -green.
GROUP II.
BUDS ALTERNATE; ARRANGED IN TWO LONGITUDINAL ROWS
ON OPPOSITE SIDES OP THE TWIGS /Fig. 27).
The following belong to this group :
Spanish chestnut.
Limes.
Hazel.
Elms.
Beech.
Hornbeam and (Birch).
I. Buds roundish -oval : each about twice as long as broad.
(A) Visible bud- scales few (one or two).
* Young twigs with longitudinal ridges or angles.
Spanish chestnut (Castanea vulgaris Lam.). Twigs deep red
or reddish-green, straight : the buds are placed not immedi-
ately above the distinct leaf-scar, but slightly on one
side.
BUDS ALTERNATE 63
** Young twigs cylindrical ; one large and one small bud- scale
to each bud.
Common lime ( Tilia vulgaris Hayne). Twigs smooth, blood-red
or orange-red, with a shining surface, somewhat long and
bowed.
Small-leaved lime (T. parvifolia Ehrh). Similar to the pre-
ceding species, but bark lighter colour and a smaller
tree.
Broad-leaved lime ( T. platyphyllos Scop. ). Twigs slightly hairy :
a larger tree than T. parvifolia Ehrh.
(B) Several bud-scales visible.
* Buds flattened on one side ; bud-scales pale, brown-
ish, or reddish-green.
Hazel (Coryhis Avellana L.). Young twigs hairy and
with a few stalked glands.
** Buds rounder and more pointed ; bud-scales dark
brown or dark maroon.
Common elm (Ulmus campestris Sm.). Young twigs
more or less hairy ; older twigs with fine rich
brown-coloured fissures on the bark. A variety
(7. suberosa Sm.) with longitudinal thick ridges of
cork is met with.
Wych elm (U. montana Sm.). Twigs and buds
similar to the preceding, but twice or three times
the sire. The leaf-scars are large.
2. Buds pointed, often three or more times as long as broad.
Beech {Fagus sylvatica L.). Twigs slender, smooth ; the
buds are usually over half an inch long, round in section,
and jut out from the stem.
Hornbeam (Carpinus Betulus L.). The buds lie closer to
the stem, and are not nearly so long as those of beech ;
they are also slightly angular in section.
Birch possesses twigs and buds somewhat similar FIG. 27. Twigof
T , , i i t i i i A-. Spanish chestnut
to Hornbeam, and although it belongs to Group showing alternate
III., it sometimes has buds nearly arranged as in arrangement of
_'__ , , .,, buds.
Group II., and may be noticed here.
Birch (Bctula alba L.). The twigs are slender and elastic : in some
varieties they are hairy, in others covered with small resinous
tubercles.
6 4
THE VEGETATIVE SHOOT
FIG. 28.
Twig of Plum
tree, showing
spiral arrange-
ment of buds.
GROUP III.
BUDS ARRANGED SPIRALLY ON THE TWIGS (Fig. 28).
To this group belong :
Birch. .Plums.
Walnut. Cherries.
, Oaks. Pear.
Willows. Apple.
Poplars. Black Currant.
Alder. Red Currant.
Black Alder. Gooseberry.
Wild Service. Raspberry.
White Beam. Blackberry.
Mountain Ash. Barberry.
Hawthorn. Wild Dog Rose
Blackthorn.
1. Pith divided into chambers.
Walnut (Juglans regia L.). Young twigs thick,
leaf-scars very large. Lateral buds small, round,
black and smooth, the terminal one much larger
and hairy.
2. Buds naked, i.e. without protecting bud-scales.
Black alder (Rhamnus Frangula L.). Young twigs
reddish.
3. Buds distinctly stalked.
(a) Apparently only one bud-scale visible.
Alder (Alnus glutitiosa Gaert.). Young twigs irregu-
larly triangular in section, brown or reddish-brown
in colour. The buds are angular, dark brownish-
red, and their stalks j-inch or more long.
(b) Several bud-scales visible.
Black Currant (Ribes nigrum L.). Twigs smooth,
pale brown or pale greyish buff; buds plump,
round, blunt at tips, bud-scales dark pink or
brownish-pink, sometimes greenish. With aid of
a lens yellow glands are visible on the bud stalks
and scales.
Red Currant (Ribes rubrum L.). Twigs with loose,
fluffy, ashy grey bark ; buds thinner, longer, and
more pointed than black currant; their scales
dark chestnut brown, with fine woolly hairs.
BUDS ARRANGED SPIRALLY 65
4. Buds sessile, with apparently only one large bud-scale (really two
united).
Willows (Salix Sp.). The willow hybridises so freely that it is im-
possible to distinguish all of them by characters of the buds and
twigs alone.
The following, however, may be mentioned :
Those with hairy buds :
Osier (Salix viminalis L.). Buds of unequal size; older twigs
smooth and shining.
Grey Sallow (S. cinerea L,). Very soft hairy twigs and large buds.
White Willow (S. alba L.). Very small buds; older twigs reddish-
grey and dull.
Those with smooth buds :
Crack or Redwood Willow (S. fragilis L.). Twigs brown and
polished ; buds almost black.
Bay-leaved Willow (S. ptntandra L.). Similar to above, but buds
brown.
Rose Willow (S. purpurta L.). Very long pointed buds.
Great Sallow (S. caprea L.). Short, plump, yellowish or reddish buds.
5. Buds sessile, each with several visible bud- scales. Twigs with
spines (hairs and emergences) upon them, but no spiny branches
present.
(a) Spines straight, situated just below the buds only.
Gooseberry (Rtbes Grossularia L.). Twigs round, light yellowish-
grey ; buds pointed and slightly stalked.
Barberry (Bcrberis vulgaris L. ). Young twigs, with slight longi-
tudinal ridges, thin ; buds bluntish at tips, and sessile.
(3) Spines with stout bases, tips bent backwards usually, and irregu-
larly arranged on the twigs.
Wild Dog-Rose (Rosa canina L.). Twigs round ; buds smooth,
roundish, blunt-tipped.
Blackberry (Rubus fruticosus L.). Twigs angular; buds hairy,
longer, and more pointed ; spines very irregularly placed.
(c) Many small soft spines, and hairs on twigs.
Raspberry (Rubus IJaus L.). Twigs pale reddish or yellowish-
brown, shining ; bud-scales loosely arranged.
6. Buds sessile ; several bad-scales visible.
(a) Bud-scales green, with narrow brown edges.
Wild Service Tree (Pytus torminalis Ehrh.). Buds oval, bluntish
tips, smooth, and somewhat flattened on one side.
White Beam (Pyrus Aria Sm.). Buds hairy at tip, longer than
the preceding, and pointed ; bud-scales keeled.
6
66 THE VEGETATIVE SHOOT
(J) Bud-scales black or dark purple.
Rowan-tree or Mountain Ash (Pyrus Autuparia Gaert.). Buds
large, often J inch long or more.
(f) Bud-scales hairy all over.
White Poplar (Populus alba L.). Young twigs covered with a
white, loose cottony film : older ones smooth, yellowish-grey ;
buds plump and pointed.
Apple or Crab (Pyrus Malus L.). Twigs partially hairy ; small
wood -buds on long shoots closely pressed to stem and triangular
in outline. In the wild or crab-apple short branches ending in
a " thorn " are present.
(</) Bud-scales smooth or hairy only at the tips or margins.
(1) Several buds crowded at the tips of the long shoots.
Common English Oak (Quercus pedunculata Ehrh.). Young
branches greyish -brown, without hairs and furrowed. The
buds stand out from the stem, are yellow or chestnut-brown
colour, quite smooth, plump, and rounded at the tips.
Durmast or Sessile Oak (Quercus sessiliflora Sails.). Young
branches slightly hairy ; buds longer than the preceding,
and their scales tipped and edged with hairs.
(2) Long narrow-pointed buds, chestnut-brown in colour, and
covered with resin at tips ; twigs furrowed.
Black Poplar (Populus nigra L.). Bud-tips straight or
pointing outwards.
Aspen (Populus tremula L.). Tips of the buds pressed close
to stem.
(3) Buds dark brown ; leaf-scar a narrow crescent.
Pear (Pyrus communis L.). Twigs smooth, yellowish-
brown ; not hairy. In wild pear short branches terminat-
ing in " thorns " are present.
Hawthorn or White Thorn ( Crataegus Oryacantha L. ). Twigs
greyish -purple or greenish-grey ; buds paler than the pear
and rounder; usually two together one large, the other
smaller. Generally spiny branches are present at the side
of the buds.
(4) Buds dark brown ; leaf-scar rounder, almost a semicircle.
* Buds small and round.
Sloe or Blackthorn (Prunus spinosa L.). Young twigs
smooth, greyish-brown ; older ones black. Buds very
small, usually two or three together.
** Buds larger and conical.
Apricot (Prunus Armeniaca L.). Young twigs greenish-
BUDS ARRANGED SPIRALLY 67
brown or reddish-green, smooth and shining ; usually three
buds together above leaf-scar.
Bullace (Prunus insititia L.). Young twigs hairy; older
ones smooth and dark brown. Bud-scales hairy.
Wild Plum (Prunus domestica L.). Young twigs smooth,
reddish or purplish brown.
*** Buds oval.
Bird Cherry (Prunus Padus L.). Young twigs thinnish,
reddish-brown. Buds large (i inch long and more) and
pointed. Bud-scales chestnut-brown, keeled, mucronate
tip.
Gean: Bigarreau and Hearts (Prunus Avium L.). Twigs
stout and short, reddish -brown and grey. Buds large and
crowded on short shoots. Bud-scales chestnut-brown ; not
keeled.
Dwarf Cherry : Morello and Kentish (Prunus Cerasus L.).
Twigs thin and slender, yellowish or greenish -brown and
grey. Buds smaller (J inch long).
Btahaleb (Prunus Mahahb L.). Buds smaller and not so
plump as the dwarf cherry : stand closer to the stem.
Twigs similar in colour.
CHAPTER V
THE LEAF.
i. As previously noted leaves arise in all cases from buds, and
are side or lateral appendages of the stems of plants. They may
be of many forms but are generally flattened structures, and, with
the exception of those known as floral leaves, usually have buds
in their axils. Their growth differs from that of the stem and
root in being of short duration, for after reaching a certain
size their increase ceases.
2. Foliage-leaf. Those which are most conspicuous upon
plants are green and are designated
foliage-leaves. They are important organs
generally concerned with the manufacture
of food needed by the growing part
of the plant, and are also organs from
which much of the water taken from the
soil by the roots is given off into the
air. A typical green foliage-leaf (Fig. 29)
consists of the following parts (i) a broad
expanded portion termed the blade or
lamina ; (ii) a slender stalk or petiole ; and
(iii) a somewhat flattened basal sheath
which connects the leaf to the stem.
The leaf-sheath often bears two appen-
dages the stipules which may be broad
and wing-like as in the clovers and pea, or small and narrow
as in pear and apple; leaves possessing them are said to be
stipulate, while those without are exstipufate.
Fro. 29. Foliage-leaf of
plum / Lamina or blade ;
p petiole ; s stipule.
FOLIAGE-LEAF 69
The parts of the leaf are of very varied form. In the grasses
the sheath completely embraces the stem, and in the Umbelliferae
(eg. carrot, parsnip, and celery) it is very prominent ; in many
plants it is scarcely visible.
The petiole where present is usually narrow and cylindrical ;
frequently it is very short or missing altogether, in which case
the leaf is described as sessile.
The blade is generally the most obvious part of a foliage-leaf
and the points of importance to notice at present are its venation,
outline, margin, apex, and character of its surface.
(a) Venation of leaf -blade. The substance of the leaf is
traversed by a number of woody strands which are termed
veins or nerves, although it must not be inferred that they
are similar in structure or function to the veins or nerves of
animals. The arrangement of these strands is termed the
venation of the leaf, of which there are two common types,
namely (i) parallel and (2) reticulate or net- venation. In the
first type the chief strands all run parallel to each other from the
base of the leaf to the tip, as in the leaves of grasses, onion,
hyacinth, lily-of-the-valley, and Monocotyledons generally.
In net- veined leaves the smaller very delicate strands form a
fine net-work within the leaf and this arrangement is charac-
teristic of Dicotyledons.
Of reticulate veined leaves two divisions are made according to
the arrangement of the main strands. In one, the leaves have a
central strand or mid-rib running down the middle of the leaf and
from it are given off slightly smaller branch strands as in Fig.
29; such leaves are pinnately veined or feather-veined, those
of the apple, plum, and peach are good examples.
In the other division each leaf has several strong strands which
start from the base of the blade and spread across to its margins
somewhat like the fingers of an outstretched hand ; such a leaf is
described z&palmatdy veined. Ivy, sycamore, and currant leaves
show this type of venation.
THE LEAF
(b] Forms of blade. The outline of the blade of the leaf may
assume almost any geometrical figure (Fig. 30). When it is
67" ^
FIG. 30. Common Forms of Leaves: i, Linear; 2, lanceolate;
3, ovate; 4, elliptical, 5, cordate; 6, sagittate; 7, hastate; 8,
reniform ; 9, spathulate.
much elongated and narrow as in grasses it is termed a linear leaf.
It may also be lanceolate as in the narrow-leaved plantain ; ovate
egg-shaped); elliptical; reniform or kidney-
shaped; cordate (heart-shaped); sagittate
(arrow-shaped) ; spathulate (spoon-shaped) as
in the daisy ; and hastate (halberd-shaped) as
in sheep's sorrel.
(c) Leaf-margin. The edge of the leaf-blade
is sometimes entire as in privet ; or variously
indented with larger or smaller incisions. (Fig.
31.) Leaves having margins like the edge of
4. 3. 2. 1.
a saw are serrate : when the small tooth-like
FIG. i. -Leaf- margin: ...
i, Entire ; 2 , serrate ; 3 , incisions stand out at right angles to the edge
dentate ; 4, crenate. . . c, -
of the leaf it is described as dentate ; the term
FOLIAGE-LEAF
crenate is used when the edge has small semi-circular prominences.
If the indentations are deeper the leaf is then described as lobed
(fid), parted (-partite), or dissected (-sect) respectively, according
as the divisions reach about one half, three quarters, or nearly
the whole way down towards the midrib.
As the indentations follow the direction of the main strands
or veins of the leaf we have two types of lobed, parted or dis-
sected leaves namely: (\) pinnatifid (i, Fig. 32) pinnatipartite,
pinnatisect and (2) palmatifid (3, Fig. 32), palmatipartite, and
palmatisect.
So long as the divisions of the blade do not quite reach to
the main ribs the leaf is said to be simple; in many cases,
however, the partitions are such that the leaf appears to have
several distinct blades; it is then compound, and the separate
parts are its leaflets (t, Fig. 32).
Compound leaves are either pinnate
as in pea, vetch, potato, rose and
ash ; or palmate as in clover, horse-
chestnut, and lupin.
(d) Surface. The surface of the
blade is smooth or glabrous, or some-
times covered on one or both sides
with hairs.
(e) Aj>ex.-~The tip of the leaf.
when it is pointed is acute; when
drawn out to a longer point it is
acuminate : it may also be obtuse
(blunt), emarginate (notched), or
. . . FIG. 32. T. Simple pinnatifid leaf ,
mucronate ; m the latter case the s bbe. 2 . Compound pinnate leaf;
. i , . . i t leaflet. 3. Simple palmatifid leaf;
midrib appears to project as a sharp , i he. 4 . Compound palmate leaf;
point see leaves of lucerne (Fig. /leaflet -
133) and trefoil.
Ex. 36. Examine and describe the leaves of the chief farm plants and as
many of the common weeds *v> possible. Observe first if they are simple or
72 THE LEAF
compound, then note the presence or Absence of stipules and petiole, aftei
which describe their form, margin, apex, and surface.
3. Modified Leaves. Structures are often met with upon
plants which although they do not possess all the parts of a
foliage leaf as just described, are, nevertheless to be regarded
as leaves on account of their origin and position upon the plant,
and also by the fact that they frequently bear buds in their
axils, and under some circumstances may become changed into
ordinary green leaves. Several of these modified leaves
receive special names as indicated below, according to their
position upon the stem, or according to their texture, colour,
and other peculiarities.
(a) Cotyledons or seed-leaves. These are the first leaves which
a flowering plant possesses, and are nearly always simple and
entire, and without stipules.
Some coniferous trees (pines and firs) have seedlings with
several cotyledons, but dicotyledons usually possess only two
(Figs. 5, 103, no), while in monocotyledonous plants only
one is present.
In the bean, pea, and vetch they serve merely as storehouses
for the food upon which the seedling depends for its early
growth. In the cereals and grasses generally, the chief work
of the cotyledon is to absorb the endosperm of the seed, and
transfer it to the growing-points of the young root and shoot ;
while in the turnip, mangel (Fig. no) and many other plants they
come above ground and carry on the work of 'assimilation,'
thus behaving as ordinary foliage-leaves.
(b) Scales. These are usually thin membranous leaf-struc-
tures, generally brown, white, or yellowish in colour, and may
be either complete leaves, or merely the sheaths and stipules of
leaves the blades of which have not developed.
On the stems above ground they are often present as coverings
to the buds of trees and shrubs, acting as a protection for the
interior of the bud against frost, heat, rUin, and the attacks of
MODIFIED LEAVES
73
t
insects. Scales are always present upon the underground stems
of perennial plants, and vary much in size. Upon the rhizomes
of couch-grass and potato, they are small and membranous,
while the leaves of a resting bulb are large scales, some of which
are thick and fleshy, and stored with food.
(c) Bracts and Bracteoles. The leaves which occur upon the
stem at points where
the flowers and inflores-
cences arise are termed
bracts and bracteoles (see
p. 89). They are very
variable in size, texture
and colour. In some
plants they cannot be
distinguished from the
ordinary green foliage-
leaves except by their
position ; more often
they are rudimentary
leaves somewhat re-
sembling scales. The
chaffy bracts surround-
ing the flowers of grasses
are termed glumes. In
Arum, Iris, Narcissus,
and snowdrop, a large
bract, termed a spathe,
encloses the whole in-
florescence.
The cup of the acorn and the husk of the filbert and hazel-
nut are persistent united bracts.
Bracts are sometimes brightly coloured.
(d) Floral leaves. The special leaves constituting the chief
parts of a flower are termed floral leaves (see next chapter).
st
Fie, 33. A single compound leaf of pea :
Stipule ; / leaflet ; t tendril.
74 THE LEAF
(e) Leaf-spines. In the sloe and other shrubs and trees certain
branches are found which have been modified into short, stiff
spines. That the latter are branches or shoots is seen from the
fact that they frequently bear small leaves and buds.
In some plants however, such as barberry, the spines are
evidently not branches, but modified leaves, for buds and stems
frequently appear in their axils, and in the barberry all stages
of transition between an ordinary green leaf and a branched
spine are frequently observable on the same plant.
(/) Leaf-tendrils. In the vetch and pea (Fig. 33) the terminal
leaflets, instead of being green, are modified into thin, thread-
like structures termed tendrils. They are sensitive to contact
and wind round any small object which they touch.
In some plants, such as the vine and passion-flower, the
tendrils are not leaves but modified branches.
Kr. 37. Examine the cotyledons of the seedlings of weeds springing up
on garden soils and arable ground. Note the difference between these and
the first foliage-leaves.
Examine the cotyledons of seedlings of the common farm crops.
Ex. 38. Examine the scales of an onion, tulip, and lily bulb, and those
upon the underground stems of couch-grass and other plants.
Ex. 39. Examine the spines on a gooseberry bush. Do they belong to
the leaves or are they modified shoots ?
Note both the leaf-spines and stem-spines upon ordinary gorse.
Compare with Ex. 29.
Er. 40. Note the form and position of the tendrils of a retch and pea,
both when free and when wound round a support.
4. Leaf-arrangement. Although to a casual observer the
leaves appear to be without any regular arrangement upon a
plant, careful inspection shows that they are distributed on the
stems in a very definite order, which is usually constant for each
species.
In some, such as the sycamore (Fig. 14), dead-nettle, and
cleavers, two or more leaves arise at the same node of the stem.
Each collection of leaves is then called a whorl> and the
LEAF-ARRANGEMENT 75
individuals comprising it are always separated from each other
by regular angular intervals. Thus, if two leaves are present
they are half the circumference of the stem apart or exactly
opposite each other, and not both on the same side; if three
arise at the same node, they are separated from each other
by regular intervals of 120 degrees, or one-third of the circum-
ference, and so on for any number of leaves.
On many stems the leaves are not in whorls but scattered
singly along it, only one leaf arising at each node : such an
arrangement is spoken of as alternate or spiral. A line drawn
from the bottom to the top of a shoot in such a manner that
it touches the base of each successive leaf is a spiral. The
distances between the leaves measured along the stem are
variable, some being an inch apart, others two or more; their
angular intervals apart are, however, as definite and regular as
in plants with the whorled arrangement.
The divergence or angular distance is usually expressed in
fractions of the circumference. In elm, Spanish chestnut and
grasses, it is ^, that is, the spiral in passing from one leaf to the
next winds half round the stem. In birch it is J, while in pear
and plum the angular distance is f of the circumference.
The divergences most frequently met with are, , , |, f , and
r Y On inspection these spirally arranged leaves are seen to be
in straight longitudinal rows along the stems; plants with a
divergence of \ having two rows, those with \ three rows, and
those with f five rows, and so on, the denominator or lower
figure of the above fractions indicating the number of rows
present.
If any particular leaf in a row is selected and the spiral traced
round the stem touching each successive leaf until another leaf
is reached on the same row, the number of leaves touched, not
counting the one at which we start, is equal to the number
of the denominator of the fractions expressing the angular
divergence, and the numerator indicates the number of com-
76 THE LEAF
plete turns round the stem which the spiral line traces. For
example, the angular divergence of the leaves on a pear shoot
is : selecting any one leaf as a starting point, the spiral line
passes twice round the stem by the time that it reaches the
next leaf on the same row, and in doing so touches the bases
of five leaves. To determine the leaf-arrangement upon any
particular shoot, it is necessary to observe the bases of the
leaves and not the blades, as the position of the latter is affected
by external conditions, especially by light and the force of
gravitation. Occasionally the stems become twisted during
growth, and the leaves are consequently displaced from their
normal position.
The orderly arrangement of the leaves upon stems is de*
pendent on the internal forces of the living plant. By growing in
this manner all the leaves become equally exposed to light and
air, and interfere very much less with each others requirements
in this respect, than would be the case if the leaves were disposed
irregularly.
Ex. 41. Examine and describe the leaf-arrangement upon the shoots of all
common farm plants, trees, and weeds.
5. Bud-arrangement. As buds arise normally in the axils of
leaves, it follows that the arrangement of buds upon trees in
winter will be similar to that of the leaves during the previous
summer. A careful recognition of the position and arrangement
of buds upon the shoots of plants is of some importance in the
practice of pruning, where buds are required to produce branches
growing in some particular direction.
For the arrangement of the buds upon the chief shrubs and
trees, see pp. 61-67.
6. Leaf fall : * Evergreens.' In most of the broad-leaved trees
and shrubs of temperate regions the leaves produced from buds
in spring usually last only one growing-season, and then all fall
off before the plants enter a state of rest iii the following winter.
LEAF-FALL 77
A number of shrubs and trees, however, appear clothed with
green leaves at all times of the year. These are described as ever-
green. In such plants the leaves produced from buds in spring are
not shed in the following autumn or winter, but live sometimes
several seasons before they die and fall off. The length of time
during which the leaf remains on a so-called evergreen tree after
it is produced depends upon the kind of tree, the climate,
situation, soil and other conditions.
In privet the leaves often remain on the twigs during winter,
and fall off when the new buds open in spring ; while in some
conifers the leaves are not shed until they are ten years old or
more.
The leaf usually separates from the shoot bearing it, at a point
close up to the latter, and a more or less conspicuous mark,
termed the leaf-scar, is left upon the shoot. The dangerous
effects of an open wound is prevented by the formation of a
protective layer of cork over the surface of the scar, which
layer originates some time before the actual fall of the leaf.
Leaf-fall is not merely the dropping off of dead, withered
leaves, but a distinct physiological process, which does not
take place in leaves which are prematurely killed by the action
of frost or excessive heat Moreover, the leaves do not fall off
from branches of trees and shrubs broken or cut off, in early
summer.
Ex. 42. Observe the manner of leaf-fall upon the common shrubs and trees,
paying special attention to those with compound leaves, such as ash and
horse chestnut.
Note the form and size of the leaf-scars.
Try and determine how long the leaves persist upon box, laurel, privet,
hotly, silver-fir, Scotch pine, and other common evergreen shrubs and trees,
CHAPTER VI.
THE FLOWER.
i, THE root stem and green leaves which have been under con-
sideration in the last three chapters are termed the vegetative
organs of the plant. Although our attention has been chiefly
directed to their morphology or origin, form and relationship to
each other, it may be remarked that the work which these
organs perform, for the benefit of the plant, is principally
concerned with the maintenance of the life of the individual
which bears them.
2. Sooner or later, however, flowers arise upon the plant, the
special function of which is reproduction : in them seeds are
produced containing embryos capable of developing into a new
generation of plants when opportunity offers.
Before discussing the work of the flower it is necessary to
become acquainted with the form and arrangement of its parts,
and for this purpose it is advisable to begin with the study of
a simple example such as a buttercup, A section through the
latter is given in Fig. 34. In the centre of the flower is seen a
stem-like axis (r) which is a continuation of \hzpcduncle or flower-
stalk. This is the receptacle of the flower and upon it is arranged
a considerable number of lateral appendages of which there are
four distinct forms present The lowermost of these appendages,
that is, those farthest away from the apex of the receptacle, are
yellowish-green in colour and resemble boat-shaped scales (m)**
There are five of them free from each other and arranged in a
whorl : each is termed a sepal, and the whole collection or whort
is known as the calyx of the flower.
78
THE FLOWER
79
Immediately above the sepals, and alternating with them, are
five bright yellow heart-shaped leaves (n) ; these are the petals,
the whole collection of which is termed the corolla of the flower.
Next to the whorl of petals are the stamens (s), of which there
are a large number. Each consists of a thin thread-like stalk
surmounted by a swollen and elongated tip. In the buttercup
the stamens are not arranged in a whorl but in the form of a
closely wound spiral round the receptacle ; the whole collection
of them is the andr&cium of the flower.
Occupying the highest position upon the receptacle is a series
of small, green, flask-shaped bodies (c) ; they are hollow and it
m
A B
B'lG. 34. A, Flower of Buttercup (Ranunculus acris L.). B,
Vertical section through the same, r Receptacle of the flower ; m sepal
of the calyx; n petal of the corolla; s btumen of the androecium ; c
carpel of the gyruucium.
is within them that the seeds of the plant are produced. Each
is termed a carpel, and the whole collection is known as the
gynacium or pistil of the flower.
3. Although the flower of a plant appears different in many
respects from anything we have yet examined it is in reality a
form of simple shoot or a stem with leaves upon it. The whole
of its parts, however, have been modified to serve the purpose
of seed production, and at first sight its likeness to a simple
vegetative shoot is not appreciated.
That a flower is essentially equivalent to a simple shoot with
80 THE FLOWER
very short internodes is, however, apparent from a study of its
origin and position upon the plant and also from an examina-
tion of abnormal or monstrous flowers which occasionally occur.
A flower always occupies the position of a shoot; it arises
either at the apex of a stem or in the axil of a leaf. Its receptacle,
which normally ceases growth in length at an early period, occa-
sionally grows on through the centre of the flower and develops
into an ordinary leafy vegetative shoot.
The sepals, petals, stamens and carpels occupy the position of
leaves upon the receptacle or axis of the flower ; they are lateral
appendages of the receptacle and are termed floral leaves. More-
over, the leaf-like character of the sepals and petals is generally
obvious, and in so-called ' double flowers ' some or all of the
stamens and carpels assume the appearance of petals.
4. Arrangement, Symmetry and Number of Floral Leaves.
When the whole of the floral leaves are arranged in whorls, the
flower is said to be cyclic : if they are inserted in a spiral line on
the receptacle, the flower is described as acyclic. The term hemi-
cyclic is applied to those flowers which like the buttercup have
some of their floral leaves in whorls and others in spirals.
Generally the successive whorls alternate with each other : the
petals for example are not opposite to the sepals, but occupy
the spaces between the latter; the stamens alternate with the
petals and the carpels with the stamens.
Very often the individual members of each separate whorl in
a cyclic flower are all alike in shape and size ; such a flower is
regular^ while those in which this is not the case, as in the pea
and violet, where some of the petals are larger than the rest, the
flower is irregular.
All those flowers which can be divided into two equal and similar
halves by a plane passing through the axis of the receptacle are
symmetrical. Usually regular flowers can be divided into two
halves by planes passing through the axis in several different
directions : they are designated actinomorphic flowers, examples
THE RECEPTACLE 8 1
of which are chickweed, poppy and wallflower. Those which
can be cut into two equal halves in one direction only are
zygomorphic ; for example vetch, pea and dead-nettle.
The number of members constituting each whorl in a flower
is subject to much variation, but it will frequently be observed
that in Monocotyledons each whorl consists of three floral leaves
or some simple multiple of three (such as six or nine). In
Dicotyledons the floral leaves are usually in fours or fives.
The pattern flower just described consists of four distinct
kinds of floral leaves and is termed a complete flower. Sometimes
flowers are met with in which one or more entire sets of floral
leaves are missing either calyx, corolla, androscium or gynaecium ;
such are spoken of as incomplete flowers : examples are seen in
the mangel and ash.
5. The Receptacle. In the Buttercup the receptacle is an
elongated cylindrical or conical axis and the whorls of floral
leaves are arranged upon it at successively higher levels, the
gynaecium occupying the highest and the calyx the lowest
points respectively, with the corolla and androecium between.
In many cases the receptacle is thicker and not so long as that
of the buttercup, but the relative positions of the parts upon it is
the same. Flowers which like the buttercup have the corolla
and andrcecium inserted on the receptacle at a lower level than
the gynaecium and free from the latter are termed hypogynous
flowers, and the gynaecium is described as superior (i, Fig. 35);
examples are charlock, poppy and chickweed.
In the plum the apex of the receptacle ceases to grow at an
early stage, but the parts below the apex grow up all round it
and form a hollow basin or urn-shaped structure, on the edge
of which the calyx, corolla and stamens are arranged (Fig. 124).
The gynaecium, consisting of a single free carpel, is placed at
the bottom of the hollow receptacle (2, Fig. 35), this point being
the real apex of the floral axis.
Flowers in which the corolla and androecium are arranged on
82
THE FLOWER
the edge of a more or less hollow receptacle, surrounding the
free gynsecium, are perigynous and the gynaecium is said to
be superior as in hypogynous flowers. The flowers of plum,
cherry, strawberry, are examples : in the strawberry, the part of
the receptacle which bears the gynaecium is a solid lump, but
round the latter the rest of the receptacle forms a flattish rim
on which the petals and stamens are borne (Fig. 125).
In some flowers the receptacle appears to be hollowed out as in
the plum, but the carpels instead of being free from it are closely
invested by its walls and completely adherent to the latter, so
that the receptacle and gynaecium appear to be one structure :
the ovaries of the carpels are imbedded in the receptacle, and
FIG. 35. Diagrammatic vertical section through I. a hypogynous flower ; II. a
perigynous flcwer ; and III. through an epigynous flower, r Receptacle ; s sepal
of calyx ; / petal of corolla ; a stamen of androecium ; o the gynaecium.
only their stigmas and upper parts are free and exposed. In
such flowers the sepals, petals and stamens, seem as if they were
produced on the upper part of the gynaecium, or its ovary,
although in reality they spring from the receptacle which encloses
and is completely united with the latter. Flowers of this type are
described as epigynous^ and the gynaecium is inferior (3, Fig. 35).
Examples are seen in the apple, pear, gooseberry and carrot.
The exact limits of the receptacle and the gynxcium cannot be
seen or understood in fully developed flowers, and in many cases
uncertainty exists in regard to them. The above description and
THE ESSENTIAL PARTS OF THE FLOWER 83
diagram (Fig. 35), however, are sufficient to enable students to
distinguish epigynous flowers from hypogynous or perigynous
ones.
6. Non-essential parts of the flower: the Perianth. The
calyx and corolla whorls of floral leaves together constitute the
perianth of the flower, and as they are not directly concerned in
the production of seeds are termed the non-essential parts of the
flower.
When one of the whorls of the perianth is absent as in the
mangel, male hop, and anemone, the flower is spoken of as
monochlamydeous ; if both calyx and corolla are absent, as in the
ash and willow, the flower is naked or achlamydeous.
(i) The Calyx. The calyx forms a protective covering for the
rest of the flower when the latter is still young, and may either
lall off when the flower opens, in which case it is caducous^ or
remain attached to the receptacle for an indefinite period, when
it is described as a persistent calyx. It is usually green but
may assume some other colour, in which case it is spoken of as
petaloid.
A calyx which consists of free separate sepals, as in the butter-
cup, is termed polysepalous ; those in which the sepals are united,
as in the primrose and pea, are said to be gamosepalous.
In groundsel, thistle, and other plants belonging to the
Compositae, the calyx takes the form of a ring of hair known as a
pappus (Fig. 148), which generally develops rapidly after the
corolla has faded and acts as a float for the distribution of the
seed-case by means of the wind.
(ii) The Corolla. This part of the flower is usually of bright
colour and serves mainly as an attraction for insects. When
the petals forming it are free from each other, as in the buttercup
and rose, the corolla is polypetalous ; the term gamopetalous is
applied to corollas which are composed of united petals, as in
the primrose and Canterbury bell.
7. The essential parts of the flower. The andrcecium and
8 4
THE FLOWER
gynaecium are directly concerned in the production of seed, as
explained hereafter (Chap, xxii.), and are termed the essential
parts of a flower.
(i) The Andrcecium consists of stamens, each of which, as
previously stated, is a modified form of leaf, although its
appearance and structure is very different from the petals and
sepals of the perianth.
A stamen usually consists of a more or less elongated thread-
like portion the filament surmounted by a swollen thicker
part termed the anther (Fig. 36).
The anther consists of two somewhat elongated halves or
anther-lobes (0), which are situated usually on opposite sides of the
upper part of the filament : the
part of the filament uniting the
anther-lobes is termed the con-
nective (c).
Running lengthwise in the
interior of each anther-lobe are
two chambers or hollow spaces
named pollen-sacs, within which
\hefollen is produced usually in
the form of loose round or oval
pollen-grains. In a young state
the latter are completely en-
closed in the anther-lobes, but
in a longer or shorter time after
the opening of the flower the
partition between the pollen-
sacs is ruptured and the anther-
FIG. 36. A, A common form of stamen.
./The filament ; a anther-lobe ; c the connec-
tive. B t View of stamen showing internal
structure. /"Filament ; c connective, on each
side of which are the anther- lobes ; /r pollen
sacs, between which is a partition d, when the
anther is young ; O n the right the anther-lobe
has dehisced, setting free the pollen-grains
p ; e empty pollen-sac.
lobes open by longitudinal slits
along the line of union of the two pollen-sacs (B y Fig. 36), the
pollen-grains being then set free in the form of dust-like powder.
In some cases the pollen-grains escape by pores or valve-like
openings situated near the apex of the anther.
THE GYN^ECIUM 85
Most frequently the stamens of the androecium are distinct
and completely free from each other as in the buttercup, but in
some flowers the filaments of the stamens are united together and
only the anthers are free. When all the filaments are united
the stamens are described as monadelphous ; if two or several
separate bundles of united filaments are present the stamens
are said to be diadelphous and polyadelphous respectively.
In the daisy, dandelion, and most plants belonging to the
Composite, the anthers are united and the filaments are free ;
such stamens are termed syngenesious.
Stamens attached to the petals, as in the potato flower, are
described as epipetalous.
(ii) The gynaecium is composed of carpels, each of which
generally consists of three parts : (i) a swollen hollow basal por-
tion termed the ovary,
(2) a thin more or less
elongated part called
the style, at the apex of
which is (3) the stigma.
The style is in many
instances missing and
the Stigma is then SeS- FIG. 37. Pod of a pea (a single carpel), v The ventral
suture ; d the d >rsal suture ; s style ; t stigmatic surface ;
Slle Upon the Upper part /funicle of the seed ; a seed.
of the ovary.
Within the cavity of the ovary are small round or oval bodies
termed ovules, which under certain circumstances to be mentioned
later develop into seeds. The part inside the ovary on which
the ovules are borne is termed the placenta,
The carpel may be considered as a leaf which has been folded
along the midrib and united at its edges. The line correspond-
ing to the united edges of the leaf is termed the ventral suture
of the carpel, and it is along this line that the ovules are generally
attached in two rows one row belonging to each edge ; the line
corresponding to the mWrib of the folded leaf is the dorsal suture.
86
THE FLOWER
These parts are readily seen in the pod of a pea (Fig. 37),
which bears considerable resemblance to a folded green leaf.
The gyngecium may consist of separate carpels as in the
buttercup, in which case it is said to be apocarpous. Frequently
the carpels are united and then form what is termed a syncarpous
gynaecium (2, Fig. 38). The amount of union among the carpels
varies, but very frequently their ovaries are completely united to
form one common ovary : in such cases the styles are generally
united to form one common style, the corresponding stigmas
usually remaining free. When the carpels of the syncarpous
FIG. ^3. i. Gynaecium, consisting of a single carpel.
v Ventral suture ; o ovules , / style ; s stigma. 2. Syncarpous
gynaicium, consisting of three completely united carpels.
o Ovary ; i style ; s stigma. 3. Transverse section of a syn-
carpous gynaecium which is unilocular. c The extent of one of
the component carpels ; the ovules are on parietal placentas.
4. Transverse section of a syncarpous gynaecmm which is
trilocular / A loculus ; d a partition or dissepiment ; c the
extent of a single component carpel ; the ovules are on axile
placentas.
gynaecium are united by their edges as at 3, Fig. 38 the ovary
possesses only one cavity or loculus^ and is said to be unilocular.
In other examples the carpels are folded so that their edges meet
in the middle of the ovary, the united parts forming partitions or
dissepiments dividing up the common ovary into several cavities
(4, Fig. 38) j such ovaries are described as m^ltilocular^ and each
loculus corresponds to a single carpel.
Occasionally the number of loculi insftie an ovary does not
MONOCLINOUS AND DICLINOUS FLOWERS 87
correspond with the number of carpels present in the latter, as
dissepiments occur which are not formed from the united walls
of two neighbouring carpels but which are produced by the
growth inwards of a portion of the ovary wall. The latter are
termed false dissepiments, an example of which is the septum
which divides the ovary in the Cruciferae.
8. Placentation. The arrangement of the placentas or points
from which the ovules arise inside an ovary is termed placentation.
When the ovules are arranged in lines on the wall of the ovary,
as at 3, Fig. 38, the placentation is parietal.
In multilocular ovaries, such as at 4, Fig. 38, the ovules are
generally arranged in the angles formed at the centre where
the edges of the carpels are united, and the placentation is
described as axile.
In the primrose and chickweed families of plants the ovules
are attached to a placenta which arises in the form of a short
column from the base of the ovary and has no connection with
the sides : this arrangement is known as free central placentation,
9. Monoclinous and diclinous flowers : monoecious and
dioecious plants. When both the essential parts are present in
the same flower, as in the buttercup, charlock, and the majority
of common plants, the flower is described as monodinous ; some-
times the terms perfect, hermaphrodite or bisexual are applied to
such flowers.
In certain flowers, as those of the cucumber, melon, hop,
hazel, and willow, one or other of the essential parts are
missing : such are said to be diclinous^ imperfect or unisexual.
Diclinous flowers may be of two kinds, namely, (i) those in
which the andrcecium is alone present and described as staminatt
or male flowers, and (2) those in which only the gynaecium is
met with and spoken of as carpellary, pistillate or female flowers.
When both kinds of diclinous flowers are met with on the
same individual plant, as in the case of the cucumber and hazel,
the plant is said to be moncecious ; in examples, such as the hop
88 THE FLOWER
and willow where the two kinds of diclinous flowers are pro-
duced on separate individuals, the plants are spoken of as
dioecious.
Ex. 43. The student should examine a large number of flowers and
specially note the peculiarities of the receptacle, calyx, corolla, androecium
and gynaecium in each : note the arrangement of the ovules within the
ovary.
He should also make himself thoroughly familiar with the terms employed
in this chapter.
Ex. 44. Examine the flowers of the bean, pea, cherry, buttercup, prim-
rose, apple, anemone, vegetable marrow, cucumber, tomato, hyacinth, tulip,
snowdrop, willow, hazel, ash, oak, sycamore, lime, oat, wheat, and any
others at hand.
Determine which are monoclinous and which are diclinous. If diclinous,
are the plants monoecious or dioecious ?
CHAPTER VII.
THE INFLORESCENCE.
IN many plants the flowers are borne singly and terminally at the
end of the main axis, as in the poppy, or singly and laterally in
the axils of the foliage-leaves of the stem or its branches, as in
pimpernel and ivy-leaved speedwell. Such flowers are described
as solitary. In most instances, however, flowers are grouped
more or less compactly together on a special shoot or axis of the
plant, as in the hollyhock, foxglove and hyacinth ; such a flower-
bearing shoot with its flowers is termed an inflorescence, and the
leaves upon it, in the axils of which the flowers arise, are known
as bracts (see p. 73). The axis of the inflorescence is termed
the rachis or peduncle, and the individual flower-stalks are called
pedicels (p, Fig. 39), the leaf-like structures upon the pedicels
being spoken of as bracteoles or prophylla.
A great variety of forms of inflorescence are met with differing
in their manner of branching, the length and thickness of their
axes, the presence or absence of pedicels, and in many other
particulars. They are conveniently divided into two groups,
namely (i) racemose or indefinite, and (2) cymose or definite
inflorescences, in accordance with the principles of branching
described on pp. 40 and 41.
I. Racemose Inflorescences.
In this type of inflorescence the main axis, or rachis, bears
either lateral sessile flowers, or flowers with pedicels, developed
in acropetal succession? that is, the youngest flowers are nearest
89
THE INFLORESCENCE
the apex and the oldest nearest the base of the rachis. If the
flowers are sessile, or borne immediately on pedicels, that is, on
lateral branches of the first order, the inflorescence is described
as simple (P'ig. 39) ; when the main axis branches more than
once before bearing the flowers the inflorescence is compound
(Fig. 41).
A. SIMPLE RACEMOSE INFLORESCENCES. In these the main
axis bears either sessile flowers or flowers with pedicels.
(i) With elongated axis and sessile flowers.
The spike (A, Fig. 39). Examples are seen in Greater Plantain
(Plantago major L. )
and Verbena.
Parts of the in-
florescences of most
grasses are small spikes
or spikelets (see p. 484).
The spadix is a form
of spike with a thick,
fleshy axis. Sometimes
a large bract, termed
a spathe, encloses this
f rm f ^florescence,
A B C
FIG. 39. Racemose, or indefinite inflorescences, with
elongated axis. A a spike ; K a raceme ; C a corymb ; ^ j^
b bract ; r rachis ; / pedicel.
(Arum maculatum L.),
white * Trumpet-Lily ' (Richardia), and many palms.
The catkin is a spike-like inflorescence, which bears only
unisexual flowers. Examples of catkins of staminate flowers are
seen in the hazel and willow ; catkins of carpellary flowers are
found on the willow.
In some plants the catkins are compound inflorescences.
(ii) With elongated axis and stalked flowers
The raceme (B, Fig. 39). In this form of inflorescence the
flower-stalks or pedicels are of nearly equul length. Examples
COMPOUND RACEMOSE INFLORESCENCES 91
are seen in the hyacinth, lily-of-the-valley, wallflower, snapdragon,
mignonette, and currants.
The corymb (C, Fig. 39) has its pedicels of different lengths,
those at the base of the rachis being longest, followed by pedicels
of decreasing length upwards ; all the flowers are nearly on the
same level. Examples occur in candytuft.
(iii) With shortened axis and sessile floivers
The capitulum or head (A y Fig. 40) possesses a short thick
rachis termed the receptacle (r) upon which are a number of
closely-packed, small, sessile flowers. Examples are seen in the
A B
FIG. 40. Racemose indefinite inflorescences with short axes.
A A capitulum ; r "receptacle" ; i involucre of bracts ; scale-like
bracteole or palea. B Simple umbel ; z involucre of bracts.
daisy, marigold, dandelion, groundsel, and all the Composite
(Chap, xxxiv.).
Usually one or more dense whorls of bracts surround the
whole head and are collectively termed the involucre of the
capitulum : in many instances a small, scale-like bract termed
a palea is also associated with each flower of the head.
(iv) With shortened axis and stalked flowers
The umbel (B> Fig. 40). In this form the main axis is short
and bears a number of flowers with stalks of similar length.
Examples occur in ivy, cowslip, and onion.
B. COMPOUND RACEMOSE INFLORESCENCES. In these the
main axis does not ^ear sessile or pedicellate flowers directly,
but bears lateral branches which are themselves inflorescences.
THE INFLORESCENCE
(i) With elongated main axis
The panicle (A, Fig. 41). In this form of compound inflor
escence the lateral branches of the main axis are racemes
or more complicated branched racemose inflorescences witl
stalked flowers. Examples occur in the vine and lilac.
The compound spike (^, Fig. 41) bears lateral inflorescence
which are spikes. Examples are seen in wheat and rye-grass.
In meadow-grasses, oats and other grasses the inflorescence
are panicles of spikelets, but are commonly termed panicle
only (see pp. 484-486).
ABC
FIG. 41. Compound inflorescence : A panicle or compound raceme : /> compoun
spike : C compound umbel. / involucre, z 1 involucel.
(ii) With shortened main axis
The compound umbel (C, Fig. 41). In this compound infloi
escence the lateral inflorescences are arranged in the form c
an umbel and are themselves simple umbels. The carro
parsnip, hemlock, parsley and nearly all the Umbelliferae (Cha{
xxxii.) furnish examples.
II. Cymose Inflorescences.
In this type of inflorescence the main axis terminates in
flower and its growth is therefore stopped. If other flowers aris
MIXED INFLORESCENCES
93
upon the axis they must spring from lateral axillary buds below
the apex. Usually each axis bears one, two, or a few branches
only, which grow more vigorously and overtop the main one :
these lateral axes terminate in flowers and repeat the same form
of branching. The terminal flower of the main axis opens first,
and is followed by those terminating the secondary, tertiary, and
other axes in regular succession.
There are a number of complicated forms of cymose inflores-
monest simpler types being :
ehasium (A and .Z?, Fig. 42) in which
its successive branches have each
cences the com
(i) The mono
the main axis and
only one lateral
branch ; exam-
ples occur in
forget - me - not
(Myosotis\ rock
rose (Helianthe-
mum)j and some
species of Ger-
anium.
(ii) The dicha- A B C
x ' FIG. 42. Cymose or definite inflorescences. A and />. Mono-
Slum Or forked chasia ; C, dichastum : i, main axis ; 2, 3, 4, and 5, axis of second,
third, fourth, and fifth orders respectively.
cyme (C, Fig. 42)
in which the main axis has two lateral branches, and each of the
latter again bear two branches ; examples are met with in stitch-
worts (Stellaria) and centaury (Erythraa).
(iii) The polychasium in which more than two secondary
branches are given off from the main axis and below each flower
of the inflorescence ; examples of polychasia are seen in many
spurges (Euphorbia).
III. Mixed Inflorescences
are frequent in which the first branches of the main axis exhibit
a racemose arrangement, while the subsequent branches are
cymose in character, and vice versd.
94 THE INFLORESCENCE
Ex. 45. The student should examine the inflorescences 01 as many plants
as possible, and determine which are racemose and which cymose in type.
Pay special attention to the position of the bracts whenever present.
He must understand that a large number of complicated inflorescences are
met with, to which no names have been given.
The structure and nomenclature of those of the simple racemose and
cymose types should be specially studied.
CHAPTER VIII.
THE FRUIT. DISPERSAL OF SEEDS.
i IT is from the flower of a plant that the fruit arises after the
completion of a physiological process known as fertilisation. A
satisfactory account of the latter and its effects can, however, only
be given after the student has become acquainted with the finer
details of plant structure ; it is therefore deferred to Chapter xxii.
It is sufficient here to remark that the process consists in the
union of a certain portion of the contents of the pollen-grain with
a minute structure termed an egg-cell situated within the ovule,
after which the latter grows and finally becomes a seed.
Soon after fertilisation has taken place, the andrcecium and
corolla of the flower usually drop off or wither up, and sometimes
the calyx falls also. The stigma and style of the gynsecium
generally wither, but the ovary in all cases remains, and grows
extensively to allow the rapid development of the seeds within it
When the gynsecium has reached its full state of development
and the seeds within its ovary have become ripe, it is termed the
fruit of the plant, and the carpel-walls of the ripe gymecium
enclosing and protecting the seeds constitute the pericarp of
the fruit
It must be observed that the term ' fruit, 1 in popular language,
is applied to a number of different parts of plants which are
often in no way connected with the ripe gynaecium of the flower,
and are therefore not fruits in this restricted botanical sense. In
the strawberry and apple, for example, the succulent edible por-
tion is the enlarged receptacle of the flower, the true fruit in the
former being the smail seed-like bodies (achenes) studded over
05
96 THE FRUIT I DISPERSAL OF SEEDS
the receptacle, while the ripened gynaecium of the apple is its
'core* (see p. 412).
The tomato, vegetable marrow, and cucumber are true fruits,
that is, they are the products of the gynaecium only, but are
nevertheless popularly designated ' vegetables/
The term pscudocarp^ or 'spurious fruit? is frequently used
for structures, such as the apple, strawberry, fig, and mulberry,
produced from a flower or inflorescence, but which include
something more than the gynsecia and their contents.
2. A complete satisfactory classification and nomenclature of
fruits is still wanting : they may, however, be divided into four
groups as indicated below, according to the texture of the
pericarp and the manner in which the seeds are set free from
the fruit.
I Indehiscent Dry Fruits.
In these the pericarp is dry and woody or leathery in texture,
and does not split or open along any definite lines. The seeds
are set free by the decay of the pericarp. As the necessary
protection for the embryo and its store of food against adverse
climatic influences and the attacks of animals, is afforded by
the strong pericarp, the testa of the seed itself is usually thin
in these fruits.
The following are the commonest forms of fruits of this
class :
(i) The nut is a one-seeded fruit, with a woody pericarp ;
it is developed from an inferior syncarpous ovary. Examples are
hazel-nut, beech-nut, acorn and Spanish chestnut.
The fruit of the horse-chestnut is not a nut, but a berry-like
capsule.
The fruit of the Composite (Figs. 147, 148) is termed a cypscla,
and is a form of nut developed from a syncarpous inferior ovary
of two carpels. Its pericarp is thin, and contains within it only
one seed ; the calyx is frequently present as a pappus.
DEHISCENT DRY FRUITS 97
(ii) The achene is a one-seeded fruit, with a thin leathery peri-
carp ; it is the product of an apocarpous superior ovary. Examples
are seen in the buttercup (Fig. 226), rose, and strawberry.
In the rose, the achenes or true fruits, are enclosed within
the hollow receptacle which, when ripe, is scarlet and soft.
In the strawberry the receptacle is succulent, the true fruits
being the small achenes studded over it (see Fig. 125).
(iii) The caryopsis is a superior one-seeded fruit resembling
an achene, but the seed within it, instead of being free as in the
latter, is united with the wall of the pericarp. The fruits of
grasses are caryopses.
(iv) The samara resembles an achene, but the pericarp is
furnished with wing-like appendages, e.g. ash, elm and sycamore
(a double samara).
n. Schizocarps.
These are dry syncarpous fruits, the united carpels of which,
when ripe, separate from each other, but do not set free the
contained seeds as in the dehiscent fruits mentioned below.
Each separate carpel of the fruit is termed a mcricarp^ and
usually contains a single seed enclosed within it.
Sycamore fruits, and those of the carrot, parsnip, and other
Umbelliferae, are examples of schizocarps (see Fig. 134).
HI. Dehiscent Dry Fruits.
In these the pericarp splits in various ways or opens by pores.
The interior of the fruit is exposed, and the seeds, which usually
have thick protective testas, are set free.
Most dry fruits of this class have many seeds.
The commonest forms of dry dehiscent fruits are mentioned
and described below.
(i) The follicle is a superior fruit consisting of a single carpel
which opens along one suture only, most frequently the ventral
one. Columbine fruits are examples (Fig. 43).
(ii) The legume is also a superior fruit of one carpel, but
9 8
THE FRUIT ! DISPERSAL OF SEEDS
it dehisces along both the dorsal and ventral lines (Fig. 37).
The pods of peas and beans are examples.
(iii) The siliqua (Fig. 44) is an elongated
superior fruit composed of two united carpels. In
the interior of the fruit is a thin false dissepiment or
partition, termed the replum, which separates the
fruit into two chambers. When ripe the two carpels
dehisce from below upwards and leave the seeds
attached to the placentas and replum. Examples
FIG. 43! Foi- are met with in the turnip, cabbage, and wallflower.
b?ne (%fK/4g?a) The term silicula is applied to fruits of this descrip-
cen*e ln a1ong e on<i ^ on which are short and broad as in shepherd's
5uture - purse.
(iv) The term capsule is generally applied to practically all
forms of syncarpous, dry dehiscent fruits except those just men-
tioned. They may be either superior or inferior,
and usually contain many seeds, The manner
and amount of dehiscence is very varied : most
frequently it is longitudinal, but in some cases
it is transverse. The dehiscence may extend a
part of the way along the fruit and the carpels
remain partially united with each other; or it
may extend the whole length of the capsule and
the carpels become free and fall away from each
other. If the latter happens and the splitting
takes place along the dorsal suture, the dehiscence
is described as locidicidal \ the term septicidal is
used when the dehiscence occurs along the line of
union of the carpels.
In some cases the outer parts of the capsules
fall off as separate pieces or valves leaving the partition or septa
of the gynaecium attached to the flowerstalk : such dehiscence
is described as septifragal.
Dehiscence by pores is seen in the capsules of the poppy.
FIG. 44. Siliqua
of wallflower,
showing manner
of its dehiscence ;
v valves of fruit ;
^replum withseeds
attached (cf. Fig.
SUCCULENT OR FLESHY FRUITS 99
The pyxis or pyxidium is a form of capsule in which the
dehiscence is transverse, the upper part of the carpels falling
off in the form of a cap or lid (Fig. 45). Examples are seen
in plantain, pimpernel, and red clover.
IV. Succulent or Fleshy Fruits.
In these the pericarp is more or less soft and sappy and, when
ripe, is usually of considerable thickness. The commonest forms
are mentioned below.
(i) The drupe is an indehiscent superior fruit of this class,
consisting of a single carpel, and usually
with one or two seeds. In the ripe peri-
carp three layers are visible, namely, (i) an
outer thin delicate skin, the exocarp or
epicarp, (2) a soft, thick, fleshy middle layer,
the mesocarp, and (3) a hard, bony layer,
the endocarp, which forms the so-called F ' G - 4S.-Pyxidjum of
* ' greater plantain (7 / ant ago
* stone' of the fruit. The seed of course is ""v r L ->' a clos ^ ; b
upper part removed arid
quite separate from the ' stone/ but enclosed showing the seeds within,
within it (Fig. 124). The fruits of the plum, cherry, apricot, peach
and almond are drupes. The individual separate carpels in
a single raspberry flower become small drupes or drupels, so
that the whole fruit is a compound one consisting of a collection
of drupels. The fruit of the walnut is a form of drupe differing
only from those above mentioned in being the product of a
syncarpous gynsecium : the endocarp develops partitions which
extend irregularly into the fleshy lobes of the single seed.
(ii) The berry is an indehiscent succulent fruit in which both
the mesocarp and endocarp are soft and fleshy. Sometimes
the berry is the product of superior ovary as in the grape,
tomato, and potato 'apple/ while in other instances it is inferior
as in the gooseberry (Fig. 46), currant, and cucumber.
' Dates' are berries the 'stone 7 of which is a true seed not to
be confused with the * Stone ' of a drupe.
100 THE FRUIT I DISPERSAL OF SEEDS
(iii) Thefonie, of which an apple or pear are good examples,
is an indehiscent
fleshy pseudocarp
whose gynaecium or
true fruit is em-
bedded in the re-
ceptacle. When the
pseudocarp is ripe
the pericarp belong-
ing to each carpel
of the gynaecium
Fit.. 46. Flower and fiuit of Rooseheiry. A the flower, develops & tOUgh,
calyx-tube, o inferior ovai y ; C longitudinal section of the IporVjprv /-vr-
flower; B transverse section of the youn^ ovary, p placenta 1CttLllci y U1
with ovules attached ; D half-ripe fruit. inner Wall it
carp the rest of the pericarp being in some cases fleshy, in
others hard and bony. Surrounding and united with these fleshy
or bony carpels is the thick, fleshy receptacle of the flower which
forms the chief edible portion of the pome (see Fig. 126 and
chapter on Rosaceae, p. 41 2).
Ex. 46. The student should watch the development of the common fruits
of the garden from the opening of the flowers to the ripe fruit.
Observe what becomes of the receptacle, calyx, corolla, and andrcecium
in each case.
He should also examine the fiuits of all useful plants of the farm, and
those of common weeds.
Careful descriptions of each should be made, noting whether they are :
(1) Dry or succulent.
(2) Dehiscent or indehiscent and manner of dehiscence.
(3) Developed from an apocarpous or a syncarpous gynaecium.
(4) Developed from a superior or an inferior ovary.
(5) One or many-celled, and the number of seeds in each.
3. Dispersal of Seeds. In some cases the ripe seeds or the
fruits containing them fall to the ground in the immediate
neighbourhood of the parent plant ; it will however, be
observed, that by far the larger proportion of plants exhibit
DISPERSAL OF SEEDS IOI
special adaptation to secure the dispersal of their seeds to
longer, or shorter, distances.
The chief agents at work in the transport of the seeds are
wind, water, and animals.
In some instances the pericarps of the fruits when ripe are
subject to spring-like tensions, and at the time of dehiscence
open, more or less violently, and scatter the seeds in all directions,
often to a distance of several feet. The ripe pods of many legu-
minous plants, such as peas, beans, and bird's-foot trefoil,
disperse their seeds in this manner, and the valves of the pods
after the opening of the fruit twist or curl up suddenly.
Fruits, which scatter their seeds by the sudden released
mechanical strains when dehiscence takes place, are also met
with on the bitter-cresses (Cardamine hirsuta L. and C.
impatiens L.) several species of cranesbill (Geranium) and
many balsams (Impatiens).
The wind is, however, the most powerful and most obvious
agency at work in the distribution of seeds, and an enormous
number of modifications are noticeable among plants to secure
dispersal by this means.
In the orchises, poppies, and other plants, the seeds are small
enough to be readily blown considerable distances in the air as
soon as they escape from their capsules. Some seeds are smooth
and round, and easily roll along the ground. More commonly,
however, the adjoining bracts or some portion of the flower, fruit
or seed, is modified in such a manner that it presents a large and
light surface to the air, and the whole structure is thus rendered
buoyant.
In many plants of the Compositae (Chap, xxxiv.), such as
thistles, groundsel, and dandelion (Fig. 148), the catyx is repre-
sented by a tuft of long delicate hairs which act as a parachute
capable of preventing the rapid fall of the fruit when once the latter
is taken up by the wind. Even in a moderate breeze the fruits
of such plants are canied long distances before they finally drop.
102 THE FRUIT I DISPERSAL OF SEEDS
In the kidney-vetch (p. 440) the calyx is large, thin, and
inflated, and in some species of clover the faded corolla is large
and of small weight in comparison with the single-seeded pod
which it encloses.
The perianth in many docks developes into thin wing-like
projections surrounding the fruit, and winged extensions of the
pericarp are seen in the ash, sycamore, elm, and certain um-
belliferous plants. Some of these fruits are of such weight that
they fall almost vertically when allowed to do so, although
with a slow spinning motion. They are, however, only de-
tached by strong winds or gales, and under these circum-
stances, may be carried considerable distances. Not only are
the external parts of the pericarp and other portions of the
flower modified for wind distribution, but the seeds themselves
of many dehiscent fruits show similar adaptations to the same
end. In the willow, poplar, willow-herb (Epilobium), and
cotton, the testa is more or less covered with long, silky,
buoyant hairs, and many seeds, such as tulip and yellow rattle
(p. 6 1 8), have thin, wing-like membraneous margins.
In the hop, and most grasses, the buoyant agents are the
bracts surrounding the fruit.
Water-plants have fruits and seeds, the bracts of which enclose
more or less air which enables them to float some distance.
A large number of seeds are spread over the earth by animal
agency. Upon the pericarp of the carrot, hedge-parsley ( Torilis)>
and other umbelliferous plants, and also that of cleavers (Galium
aparine\ and many medicks, spinous and hook-like structures
are present, which cling to the fur, wool and feathers of animals.
Similar hook-like projections are seen also on the receptacle of
agrimony and on the involucral bracts of the common burdock
(Arctium Lappa L.). Eventually the fruits are rubbed off or fall
off the animal's coat in another locality from that in which they
were collected ; in this manner seeds may be transported long
distances.
DISPERSAL OF SEEDS 103
Moreover a number of succulent fruits are eaten as food by
animals of various kinds, especially birds, and the seeds of such
fruits pass through the stomach and intestines without injury.
The protection of the embryo against the action of the
digestive liquids of the body is generally afforded by the hard
parts of the pericarp, or the seed coats. The alluring or
attractive succulent parts of the fruit in drupes cherry, sloe, and
plum, and in all berries, is the pericarp, or some part of it, while
in the strawberry, rose, apple, and hawthorn, the receptacle
is the attractive portion.
In the stone-fruits and hawthorn the hard, bony endocarp
protects the embryo while passing through the body of an
animal, and in berries the testa of the seed serves the same
purpose. In the strawberry and rose-hip the seeds are pro-
tected by the hard pericarp of the achenes.
It will be noticed that when the seeds are unripe and unfit
for dispersal the parts of the fruit used as food in all these cases
are at first green, sour, and firm in texture. But at the time of
ripening of the seeds, or soon afterwards, when they are ready
for distribution the parts of the fruit change to some conspicuous
colour, become softer and sweeter, and often develope a distinct
and characteristic odour.
Ex. 47. Examine the fruits of common weeds and endeavour to find out
how the seeds are dispersed in each.
Ex. 48. Notice the number and kinds ot seeds and fruits attached to the
wool of sheep ; also to the fur of dogs after passing through a dense copse in
summer or autumn.
What means of attachment do the fruits exhibit ?
Ex. 49. Look out for evidence of the dispersal of seeds by birds :
(a) Examine the excreta of fieldfares and thrushes in winter,
() Observe the kinds of shrubs and trees which grow sometimes on
the face of cliffs and walls of old ruins. Have they mostly
succulent fruits?
(c) What kinds of fruit have the plants found growing away from the
ground on ojd trees?
PART II.
INTERNAL MORPHOLOGY (ANATOMY).
CHAPTER IX.
THE PLANT CELL: CELL-DIVISION: TISSUES.
i. IN the preceding chapters we have been concerned with
the larger external features of the bodies of flowering plants.
It is now necessary to study the internal and minute structure
of root, stem, leaf and flower in order that the physiology, or
the work which each of these organs carries on may be satis-
factorily understood.
2. A knowledge of the internal structure is obtained by cutting
thin slices of the various organs with a
sharp razor, and examining these slices or
sections as they are called with the naked
eye and with the microscope. For a
complete understanding of the nature and
relationship of the several internal parts
of any plant organ, it is not sufficient
C to examine a section through it in one
direction only : sections must be made in
several directions. In stems, roots, and
other parts, which are longer than broad,
it is usual to make sections in the manner
indicated in Fig. 47. Those cut at right
angles to the main axis as at C, are
termed transverse sections : those which are . cut parallel to
the main axis are longitudinal section '5 u the terms radial and
104
THE CELL
105
tangential being added respectively to the latter according as
the sections pass through the centre of the stem as at A> or
not, as at B.
3. The Cell. If a very thin section of a turnip ' root ' is
examined with a microscope a kind of net-like structure is seen
as in Fig. 48. By further examination of slices taken in several
different directions, a
similar appearance is
observed in each case,
from which we con-
clude that the sub-
stance of the turnip
is composed of an
enormous number of
very small more or
less cubical or spheri-
cal compartments sur-
rounded by thin
walls. These closed
chambers are called
cells. Although they
vary in size they
are usually quite in-
. ., . , -i j FIG. 48. Cells from the fleshy 'root' of a turnip, a Cell-
VlSlDle tO the Unaided wall; s cell-cavity; n nucleus; i intercellular space. (Eu-
i , larged 180 diameters.)
eye, being rarely more
than YJ-tf of an inch and not unfrequently as small as J^TT of an
inch in diameter. A full-grown living cell (C, Fig. 49) taken
from near the apex of a root or stem is seen to consist of the
following parts :
(i) A thin completely closed membrane (a) termed the cell-
wall ;
(ii) A continuous lining (r) of a substance known as proto-
plasm ; and
(iii) A central space (v\ the vacuole^ which appears to
io6
THE PLANT CELL
be empty, but which is filled with a, watery liquid termed
cell-sap.
(i) The cell-wall is formed of a solid, elastic and transparent
dead material, called cellulose by chemists ; it acts as a protective
covering for the protoplasm and is manufactured by the latter.
(ii) The protoplasm, which is the most important part of the
cell, is a more or less slimy or jelly-like substance containing
Jl
Fig. 49. A) Very young cell from near the tip of a root. .#, Two older
cells. C, Single full-grown cell ; a cell-wall ; r cytoplasm : n nucleus ; /
plastids; v vacuole. (Enlarged about 350 diameters.)
a considerable proportion of water. Its chemical nature is not
understood, but within it there always appears to be a complex
mixture of protein compounds. It is the substance directly
associated with the peculiar phenomena which we call life.
The process of respiration, and all the remarkable chemical
changes involved in ' assimilation ' and nutrition generally, are
due to the protoplasm, as well as the powers of growth and
reproduction possessed by living organisms of all kinds, plants
and animals alike. Wherever life is, protoplasm is present, and
death implies its decomposition or destruction.
PROTOPLASM 107
In many cells the living protoplasm exhibits a characteristic
spontaneous movement ; in some instances it flows in one
direction in a continuous stream round and round the cell, in
others, currents in several different directions are observed in the
protoplasm.
From Fig. 49 it is seen that the protoplasm of the cell is
not homogeneous, but consists of the following parts :
(a) A dense more or less spherical or oval portion (), the
cell-nucleus ;
(b) A number of smaller bodies (/), termed plastids or
chromatophores \ and
(c) A more liquid and finely granular substance the cell-plasm
or cytoplasm (r), in which the nucleus and plastids are always
imbedded.
In very young cells (A, Fig. 49), the protoplasm entirely fills the
cell-cavity and it is only after the growth of the cell that vacuoles
appear. In the majority of living cells of the higher plants a
single nucleus is present in each; in some long cells, how-
ever, several nuclei are frequently found.
All nuclei arise by the division of previously existing nuclei.
Their functions are not completely known, but cells artificially
deprived of them soon die. As the essential part of the sexual
fertilisation process consists in the union of two nuclei it is
thought that the latter are the carriers of the hereditary characters
of the parent organisms from which they are derived. Moreover,
in cell-division which results in multiplication of cells the nucleus
seems to initiate and control the process of division.
The thin lining of cytoplasm, or the primordial utricle as it is
sometimes called, controls the passage of soluble substances into
and out of the cell-sap filling the vacuole.
The plastids are small bodies of protoplasm resembling nuclei
in density : three kinds are recognised, namely
(a) chloroplastSy (b) chromoplasts^ and (c) leucoplasts.
They always arise frftm previously existing plastids by division
108 THE PLANT CELL
and like the nucleus are never produced de novo. The chloro-
plasts, sometimes known as chlorophyll-granules , are green, their
substance being saturated with a green-colouring matter named
chlorophyll. All green parts of plants owe their colour to the
chloroplasts in their cells, and the very important * assimilation '
process (chapter xvi.) is due to their activity.
The chromoplasts, which are frequent in the cells of flowers
and fruits, are yellow or red, instead of green, the parts of the
plants in which they occur being rendered conspicuous by them
and attractive to birds and insects.
The term leucoplast is applied to all colourless plastids:
examples are met with in roots, tubers and other underground
parts of plants. They possess the power of forming starch-grains
from sugar. The three kinds of plastids are convertible into one
another ; the chloroplasts of green unripe fruits usually become
chromoplasts when the fruit is ripe, and the leucoplasts of a
potato tuber become green when the latter is exposed to light.
(iii) The cell-sap filling the vacuole of the cell consists of
water in which a number of substances are dissolved. In the
cells of beetroot, as well as in many fruits, flowers, and leaves,
the cell-sap contains a purple or reddish colouring-matter ; most
frequently, however, it is colourless. It is generally acid, but the
nature and amount of the compounds present in it often varies
from cell to cell in different parts of the same plant. Various
products of the activity of the protoplasm, such as sugars, soluble
proteid, acids, and organic salts, are commonly present, as
well as nitrates, sulphates, phosphates, and other inorganic com-
pounds, absorbed from the soil.
Most of the peculiar taste of the fruits and vegetables we eat
is due to the substance dissolved in their cell-sap, the protoplasm
and cell-wall being tasteless.
4. The cells of the body of a plant at the time of their forma-
tion at the growing-points of the root and stem, are all about the
same size and cubical or polyhedral' in form. They soon
THE CELL-SAP
109
increase in size and become variously modified in shape and
structure in accordance with the special functions which they
have to perform in the fully-developed organs of the plant.
If during growth the cell-wall increases in all directions alike,
the original cubical or polyhedral form is maintained ; most
frequently, however, growth is irregular and the cells assume a
great variety of shapes, the chief of which will be mentioned
when dealing with the organs of the plants in which they occur.
A great many cells after a time lose their protoplasmic contents
and nothing then remains except the cell-wall and the cell-cavity
FIG. 50. Diagrammatic illustration of thickened cell-wall; A t uniformly thickened
wall ; K, wall with simple pits; C, wall with bordered pits.
generally filled with air To these empty shells the term cell is
commonly applied although some other term would be more
suitable. Sometimes the cell-walls remain thin, but very often
they become greatly thickened before the cell completely loses
its protoplasm; such thickened cell-walls give firmness and
strength to the structures which contain them and act as
mechanical supports for the delicate parts of the plant
The thickening consists in the deposition of successive layers
of some form of cellulose on the inner surface of the cell-wall.
1 10
THE PLANT CELL
Sometimes the layers are disposed uniformly all over the inside
as in A) Fig. 50, but more frequently the increase in thickness
goes on at some points more rapidly than at others. In some
cases small areas of the cell-wall are left unaltered ; these thin
places appear as bright spots termed pits when a surface view of
the cell is examined. In simple
<^ ~^> fC^^Sl pits (B) the cavity left unthickened
I ^ : r~\ kxj: . ' -d is roughly cylindrical and viewed
end on appears as a circle or ellipse.
The cavity left unthickened in a
bordered pit is funnel-shaped, and
in surface view appears as two
concentric circles or ellipses (C).
The pits of one cell-wall are gener-
ally exactly opposite the pits of an
adjoining cell-wall, and serve as a
means of communication between
the two cells.
Thickening in the form of spiral
and annular or ring-like bands is also very common (Fig. 51).
5. Cell-division : Mitosis: continuity of protoplasm. With
the extension in length of the stem and root, and the production
of new organs at the growing-points of ordinary green plants,
a great increase in the number of cells takes place. This cell
increase is the result of division of previously existing cells, all of
which in any individual plant have originated from the division
of a single cell, namely, the fertilised egg-cell of the ovule.
During the process of division of a cell at the growing-point of
a shoot or root, the nucleus first divides into two exactly similar
halves. The two halves or daughter-nuclei then recede from each
other a short distance in the dividing cell, and a new cell-wall arises
midway between them. The new cell-wall divides the cytoplasm
into two distinct parts, and is always placed at right angles to a
straight line drawn from one nucleus to the other (Fig. 52).
FIG. 51. Portions of vessels show-
ing (i) annular, (2) spiral thickening
of their walls.
TISSUES iioa
This process of division of a cell into two daughter-cells, termed
mitosis, is complicated, and for a detailed account of it textbooks
of cytology must be consulted ; it is sufficient here to refer briefly
to the most important changes which take place in the nucleus
when a living cell undergoes such division.
In the so-celled resting stage, the nucleus is a spherical, or ovoid
body, containing within a thin membrane, a variety of substances
and structures, whose composition and arrangement need not be
discussed here.
By ' fixing ' the cell in certain chemical solutions, and staining
it with various dyes at the time when the dividing process has
begun, a long, thin, coiled thread is seen within the nuclear
membrane (Fig. 520). Later this thread contracts and thickens,
and then breaks into short pieces the chromosomes each of
which is split lengthwise into two halves exactly similar in form
and structure.
The split chromosomes soon take up a regular position in the
middle of the cell, as in Fig. 5 Fig. 52^, the nuclear membrane, in
the meantime, having disappeared.
The halves of each chromosome then separate from each other,
one set of halves moving to one pole of the cell, the other corre-
sponding set to the other pole, where they ultimately become
incorporated into two new nuclei. Between the latter a cell-wall
is formed, the original cell becoming completely divided into two
daughter-cells each containing exactly the same number of
chromosomes as the parent.
The lengthwise division and separation of the chromosomes in
mitosis ensures that the daughter-cells shall not only receive the
same number of chromosomes as that possessed by the parent cell,
but that each cell shall receive an equal share of every part of each
chromosome.
Chromosomes differ much in size and shape, and the number
present in the vegetative or somatic cells of different species of
plants varies between wide limits.
The following are the chromosome numbers in a few common
plants :
Crepis virens . 6 Mangold . .18
Broad Bean . 12 Cabbage . . 18
Pea . . .14 Turnip . . 20
Barley . . .14 Macaroni Wheat . 28
Onion . * . 16 Bread Wheat . 42
nob
THE PLANT CELL
The number is always even, for there are always present in each
cell two sets of chromosomes each composed of an equal number,
one set coming from the male, the other from the female side
7 8
FIG. 5a. Diagram illustrating mitosis of a vegetative cell, i, cell with resting nucleus;
a, nucleus with coiled thread (spireme) ; 3, four chromosomes arising from transverse
divisions of spireme, two (a 1 ) being derived from one parent, two (a*) from the other:
4, the chromosomes split longitudinally ; 5, chromosomes at centre of cell (equatorial
plate) ; 6, their separation ; 7, nuclei of daughter-cells, each with four chromosomes as in
the parent cell ; 8, daughter-cells with resting nuclei.
(4, Fig. 5 2 a) ; thus the chromosomes in the body cells of a plant
or animal exist in pairs, the individuals of each pair being homolo-
gous or exactly alike in form, structure and chemical composition.
A study of the process of the formation of the gametes or
TISSUES
ill
uniting cells taking part in fertilisation will make these facts
clear (see p. 279).
From ordinary examination of cells and their contents, it
might be concluded that
the living material of a
typical plant-cell is com-
pletely shut off by the
cell-wall from communi-
cation with its immediate
neighbours.
It has, however, been l 2 3
shown thit in a number of FlG> 52 --i- Youn K cell previous to cell-division ;
snown inai manumoer or ^ the , amea ft<-rdiv.s.on of the nucleus; 3 , cell-
instances, the protoplasm division completed (enlarged 500 diameters).
of one cell is connected with that of adjoining cells, by means
of extremely delicate protoplasmic strands which pass through
minute openings in the cell-walls, and it appears very probable
that the whole protoplasm of an organism is continuous.
In some instances, as in the embryo-sac of the ovule, the suc-
cessive division of a nucleus and its associated cytoplasm goes on
fora time without being immediately followed by the formation of
corresponding cell-walls ; sooner or later, however, the protoplasm
of almost all vegetable cells becomes enclosed in a cell-wall.
6. Tissues. The body of a plant consists of a vast number of
cells of very varied forms. These different kinds of cells, instead
of being distributed uniformly through the plant, are associated
together in the form of bands, plates and cylindrical masses :
such associated groups of cells are spoken of as tissues. The
latter may be classified in many ways according as we take into
consideration their origin, structure or function. A tissue con-
sisting of thin-walled living cells which are embryonic and capable
of division is termed a meristem or formative tissue^ the fully-
developed adult tissues being spoken of as permanent.
Taking into consideration the form of the cells composing
them, two chief types *)f tissues may be distinguished, namely,
9
112 THE PLANT CELL
parenchyma and prosenchyma. Between them no sharp distinction
can be made, but the former usually consists of cells which are in-
dividually much the same in length, breadth and thickness, and
each cell is united to its neighbours by broad flat ends and sides.
Although in young tissues all the cells are in complete contact
at all points of their surfaces, in permanent parenchymatous tissues
the common cell-walls of adjoining cells frequently separate from
each other at the angles and give rise to intercellular spaces (/, Fig.
48), which are generally rilled with air. It is important to note,
however, that in some cases intercellular spaces arise through the
complete dissolution or drying-up of masses of cells in which
instances the cavity left is most commonly filled with gums, oils,
resins and other excreted products.
The cells of prosenchymatous tissue are long and pointed at
both ends ; moreover, the ends dovetail between each other and
fit closely without intercellular spaces. Prosenchymatous and
parenchymatous tissues, whose cell-walls are thickened and hard,
are distinguished as sclerenchyma.
Ex. 50. Take one of the inner fleshy leaves of an onion bulb, and, after
making a shallow cut into the surface with a sharp knife, tear or strip off a
small portion of the ' skin.' Place it in eosin solution or red ink for a few
minutes : then wash it and mount in a drop of water on a glass slide.
Examine with a microscope, first using a low, and subsequently a higher
power. Notice and make drawings of the cells, their cell- walls, stained
nuclei, protoplasm, and vacuoles.
Ex. 51. Cut very thin slices of a turnip with a sharp razor and examine
in a similar manner ; observe the intercellular spaces between the cells. Cut
slices of A coloured beet-root : examine without staining, and notice the
coloured cell -sap.
Ex. 52. Make and examine a section of Elder pith : observe the form and
size of the dead cells and also the thickness and markings of the cell-walls.
Ex. 53. Make transverse and longitudinal sections of the wood of an
ordinary safety match, notice the thickness and markings of the cell-walls.
Examine in a similar manner pieces of other common woods.
Ex. 64. Cut thin slices of the leaves or any green part of a plant :
examine the cells and notice the greenness is not due to coloured cell -sap,
but to the existence of numerous small green chloroplasts.
CHAPTER X.
THE ANATOMY OF THE STEM, ROOT, AND LEAF.
WE propose in the present chapter to discuss the general
arrangement and structural character of the various ordinary
tissues in the different plant organs and incidentally to mention
their uses in the economy of the plant leaving the more detailed
account of physiological processes for subsequent chapters.
THE STEM.
A. The Herbaceous stems of dicotyledons.
A great portion of the herbaceous stems of dicotyledons consists
of soft succulent tissue, in which are imbedded a number of
thin, tough, stringy strands termed vascular bundles. The latter
give firmness to the stem, but their chief function is the conduc-
tion of sap to all parts of the plant.
Covering the surface of the stem
is a thin skin or tissue of cells called
the epidermis. To the remainder of
the tissues, that is, to all except the
epidermis and vascular bundles, the
term fundamental or ground tissue is
applied.
In a transverse section of the stem
the vascular bundles are seen to be
arranged side by side in a circle
(Fig. 53). That part of the fundamental tissue enclosed by the
ring of vascular bundles is spoken of as the medulla QI pith (/),
the part outside the ring is the cortex (c), while the small narrow
113
114 ANATOMY OF STEM, ROOT AND LEAF
bands running radially between the bundles and connecting the
cortex with the medulla are the medullary rays (m\
The vascular bundles, together with the medullary rays and
pith, form a cylindrical mass of tissues known as the vascular
cylinder or stele, which extends continuously throughout the
plant from the tip of the stem to the growing-point of the
root.
(i) The epidermis is usually one cell thick and acts as a pro-
tective coat for the plant, preventing the latter from too rapid
loss of water and also defending the delicate internal cells of the
plant against mechanical injuries due to rain, hail, frost and
insect attacks.
The cells are tubular flattened cells fitting quite closely to-
gether, except where the openings named stomata occur : as
the latter are more abundant in the epidermis of a leaf, their
structure is deferred to page 145. Usually the outer cell- wall
of each epidermal cell is much thicker than the lateral and
inner walls, and is differentiated into two or three layers, the
outermost layer in contact with the atmosphere being spoken of
as the cuticle. The cuticle is composed of a substance known as
cutose, which is very impervious to water, and a remarkably stable
body capable of resisting the action of various solvents which
dissolve ordinary cellulose.
On the cuticle of the stems and leaves of cabbages, swedes, and
many varieties of cereal and other grasses, as well as on grapes
and plums, an ash-coloured bloom is seen. It is an excreted
product of the epidermal cells, and consists of minute round,
rod-like or scaly particles of wax. Surfaces of the different parts
of plants covered with this bloom lose less water than those
from which the substance has been removed by rubbing.
This waxy layer appears also to act as a partial protection
against the attacks of fungi and insects.
The cells of the epidermis contain the usual cell-contents
with the exception of chloroplasts which are generally missing j
CORTEX IIS
they are especially rich in cell-sap, which is often tinted pink,
red or purple by a colouring matter which appears to protect the
cells of the cortex from excessive light. In some plants, if not
in all, the cell-sap of the epidermal cells functions as a store
of reserve water upon which the more internal cells of the stem
can draw in time of need.
It is well known that the surface of stems and other parts of
plants are frequently covered with hairs. These belong to the
epidermis, and in their simplest form are merely single cells
which have grown much longer than their neighbours. Some
hairs are, however, multicellular extensions of the epidermis
(h, Fig. 54), and like the unicellular hairs may assume a great
variety of shapes.
Hairs are often harsh to the touch, and furnish a means of
defence against insects and animals generally. They also act as
a mantle which prevents too rapid escape of water from the
plant, and acts as a screen against excessively bright sunshine.
In young stems and buds, hairs protect the tender parts
against injury by frost. Certain hairs function as secreting
organs, and are then designated glands (Fig. 106) : they often
produce resinous and oily compounds, which in the case of
mint, hop, and other plants have a characteristic odour. Many
excreted products of such hairs are sticky, and effectually prevent
insects such as ants from climbing up the stem and getting
at the nectar of the flower.
(ii) The cortex of the stem extends from the epidermis to
the vascular cylinder. A great part of it generally consists of
living parenchymatous cells which contain abundant chloroplasts.
The cells of the portion immediately beneath the epidermis
frequently have their cell-walls thickened at the corners, and
form what is spoken of as collenchymatous tissue : the latter serves
to strengthen the epidermis, and gives rigidity to the whole
stem. The innermost layer of cells belonging to the cortex
forms a continuous sneath surrounding the vascular cylinder
Il6 ANATOMY OF STEM, ROOT AND LEAF
termed the endodermis (<?#, Fig. 54) ; its cells are not very much
differentiated from the rest of the neighbouring cortical cells, but
they usually contain numbers of starch-grains which render them
somewhat conspicuous in sections of certain stems.
(iii) The vascular cylinder or stele includes all the tissues
inside the endodermis, namely, the vascular bundles described
below, and also the medulla or pith and the medullary rays.
FIG. 54. Transverse section of the stem of a sunflower (enlarged
about 8 diameters.) Jf, portion including a vascular bundle ; e epi-
dermis ; h a hair ; c cortex ; en endodermis ; w wood ; b bast ; fc
fascicular cambium ; ie interfascieular cambium ; b pericycle fibres;
m medulla or pith.
The outermost portion of the stele which lies immediately
in contact with the endodermis is known as the pericycle. The
latter may consist of a single layer of cells or of more than
one layer; in some stems, its cells are thin-walled, and from
it arise most adventitious roots and shoots.
The medullary rays and pith are composed of thin-walled
parenchymatous cells ; the cells of the medullary rays generally
retain their living contents for a long-time, but those of the
pith live for a short time only.
VASCULAR CYLINDER OR STELE n;
If we select an individual bundle in the internode of almost
any dicotyledon and trace it upwards it will be found to pass
out of the stele across the cortex and into the leaves, where it
branches and forms the veins. Bundles of this kind common
to both leaf and stem are termed common bundles^ that part of
each present in the stem being spoken of as the leaf-trace of the
bundle. From each leaf one or several bundles may enter the
stem, and on being followed downwards they are found to
descend perpendicularly through one or more internodes, finally
uniting with bundles which have entered the stem from older
leaves lower down. The bundles in their descent all keep about
the same distance from the centre, so that in a transverse section
they appear arranged in a circle.
Great variation exists in the manner and amount of branching
and union of the bundles in different plants, but the arrange-
ment is always such that the vascular bundles of the leaves,
stems and roots form a continuous conducting system of tissues
specially adapted to facilitate rapid and easy transmission of sap
to all parts of the plant.
In this type of stem each vascular bundle consists of three
kinds of tissue, namely :
(1) xylem or wood (n, i, Fig. 55);
(2) phloem or bast (d) ; and
(3) a thin-walled meristem tissue termed the cambium of
the bundle (c).
These tissues are arranged side by side in such manner that
in a transverse section of the stem a radius drawn from the
centre to the outside passes through all three; the cambium
lies between the wood and the bast, the wood being nearest
to, and the bast farthest away from the pith.
Bundles in which the wood and bast lie on the same radius
are termed collateral bundles ; when as in dicotyledons they
also possess cambium they are said to be open.
(a) Wood or xylem. The structural elements met with in the
wood
fast
FIG. 55. i. Transverse section of a vascula^ bundle of a sunflower
stem (enlarged about 12 "
2. Longitudinal radial
n the wood; d the bast , .
f fibre ; o pitted vessel ; s sieve tube ; t companion-cell ; b pcricycle fibres;
120 diameters). Enlargement of X J" previous fig.
lal section through the same. / Medulla of stem ;
bast ; c the cambium of the bundle ; a spiral vessel ;
VASCULAR CYLINDER OR STELE 119
wood are usually (i) vessels or trachea ', (2) tracheids^ (3) fibres
and fibrous cells, and (4) wood-parenchyma, all of which
commonly have much thickened firm cell-walls consisting of
lignocellulose. The proportion is not the same in all bundles
and in some cases certain structures are missing altogether ;
tracheae or tracheids, however, are constantly present in all wood.
The vessels or trachea (a and o) are not cells, but long con-
tinuous open tubes, each formed from a row of superimposed
cells, many of the transverse cell-walls of which have been ab-
sorbed or dissolved away. In some climbing plants the cavities
of the vessels are 9 or 10 feet long : according to Adler's
measurements, the vessels of oak wood average about 40
inches long, those of hazel and birch about 5 inches. Their
walls always exhibit either annular, spiral, or reticulate thicken-
ing or pits. Those first formed in the bundle possess only
annular or spiral thickenings, and constitute the protoxy-
lent.
At first all vessels contain protoplasm, but during their growth
the living substance is used up in the thickening of the cell walls:
when fully formed they are dead empty structures which serve
for the conduction of water.
Tracheids resemble vessels in the character of their cell-walls
and in their function : they are, however, long, single, empty
cells and not compound structures.
The fibrous cells are long and pointed at both ends ; they
possess living contents and their cell-walls are most frequently
thickened and sometimes marked with small pits. Fibres (/)
are similar thick- walled cells which have lost their protoplasmic
contents and contain air or water only.
The wood-parenchyma consists of somewhat elongated cells
with square, blunt ends and living contents : the cell-walls are
thickish and slightly pitted. In these cells starch is often stored.
() Bast or phloem. The elements composing the bast or
phloem are (i) sieve-tube* or bast-vessels (s) with their companion
120 ANATOMY OF STEM, ROOT AND LEAF
cells (/), and (2) a certain amount of thin-walled bast-parenchyma ;
their cell-walls consist of ordinary cellulose.
The bast-vessels are long thin-walled cells arranged end to end,
The transverse or end-walls which separate one vessel from
another, are not completely absorbed as in the vessels of the
wood, but merely perforated by open pores through which the
contents of adjoining vessels are in 'continuous open communica-
tion : these transverse perforated walls are called sieve-plates.
When mature the bast-vessels contain a thin lining of cytoplasm
but no nucleus : the rest of the cell-cavity is filled with an alkaline
slimy substance, rich in proteids, and frequently containing
starch-grains as well.
The bast-vessels serve for the conduction of various complex
organic substances, but more especially for those of a proteid
character.
The companion-cells are long narrow cells which lie alongside
the sieve-tubes : they are filled with granular cytoplasm in which
a nucleus is always present. Both the sieve-tube and its com-
panion-cell arise from the same mother-cell.
(c) Cambium. The cambium lies between the wood (t, Fig.
55) and the bast, and consists of a layer of thin-walled meris-
tematic cells, each of which has the form of a long, narrow,
rectangular prism with obliquely pointed ends.
In young stems the cambium is confined within the vascular
bundles, but in older ones a new and exactly similar meris-
tematic tissue termed the interfascicular cambium arises in the
medullary rays, and extends across the latter, joining the
cambium of one bundle with that of the next (/V, Fig. 54). We
thus have in the older stems a thin complete cylinder of dividing-
cells which in transverse section appears as a narrow zone, spoken
of as the cambium-ring.
The cambium-ring adds new elements to the wood and bast
of the stem in a manner explained below ; but in short-lived
herbaceous dicotyledons this additional growth soon ceases, so
VASCULAR CYLINDER OR STELE 121
that its effect is not so noticeable in these as in perennial woody
stems.
Ex. 55. Cut across the young soft stems of the sunflower, Jerusalem arti-
choke, groundsel, bean, potato, and any other common herbaceous plants.
Examine the cut surfaces with a pocket lens, and observe the presence and
arrangement of the vascular bundles and pith.
Ex. 56. Place some young sunflower stems in a mixture of two-parts methy-
lated spirit and one-part of water. Keep them in this mixture for further
use. From a stem which has been in the mixture three or four days cut
very thin transverse sections with a razor wetted with the mixture. Transfer
the sections to a watch glass containing water ; after remaining in the water
for a few minutes, take one out and mount it in a drop of water on a glass
slide. Cover with cover-slip and examine with the lowest power of the
microscope.
Make drawings indicating the position and general character of the
(a) epidermis,
(6) cortex,
(c) endodermis,
(d) vascular bundles,
and ((} pith and medulla; y ray tissue between the bundles.
Examine with a high power, and make sketches of small portions of the
various parts above-mentioned, paying especial attention to the wood,
cambium and bast (compare Fig. 55).
Try and see if the interfascicular cambium has been formed across the
medullary rays.
Ex. 57. Take a piece of sunflower stem about a quarter of an inch long,
preserved as in preceding exercise, and cut longitudinal sections so as to
pass through a vascular bundle. (In cutting longitudinal sections of stems,
the razor should cut from one side of the stem to the other, not from end
to end.)
Examine first with a low and then with a high power : make sketches of
the form of the cells met with in the epidermis, cortex, bast, cambium, wood
and pith respectively.
Try and determine which cells of the longitudinal section correspond with
those seen in the transverse sections.
Ex. 58. Make a careful study of the anatomy of a stem of groundsel,
bean, and other common herbaceous dicotyledons.
Always begin the examination of sections with the lowest power at dis-
posal, namely, with the naked eye or a good pocket lens. After the general
arrangement of the chief tissues is understood, then apply higher powers in
succession.
122 ANATOMY OF STEM, ROOT AND LEAF
B. The perennial woody stems of dicotyledons.
(a) Division of the cambium-cells. In the earliest stages of
the stems of shrubs and trees the arrangement and constitution
of the tissues are essentially the same as in simple short-lived
herbaceous stems. With an increase in age there is, however, a
steady increase in thickness from year to year, and in transverse
sections of such thickened stems the isolated small vascular
bundles, so obvious when the stems are very young and soft,
are no longer visible.
The greatest part of the increased bulk of tissues in such stems
as these, is brought about by divi-
sion of the initial cells of the
cambium-ring.
Each initial cambium-cell (a,
Fig. 56) divides in two by a wall
parallel to the surface of the stem ;
one of these two daughter-cells
remains capable of division while
the other is either directly con-
verted into a permanent cell, or
divides once or twice, after which
the cells produced become gradu-
ally changed into permanent
structures. The change into a
permanent cell or cells may hap-
pen to either of the two produced by division of the initial
cell ; if the inner one is modified it is added to the wood (w), if
the outer one is altered it goes to increase the bast (b).
Division of the cambium-cells, and the growth and development
of the products continue from spring to autumn ; in winter, cell-
division ceases. Since the cambium extends in the form of a con-
tinuous cylinder within the mature stem, a new cylinder of wood
is added every growing season to the outside of that already
FIG. 56. Transverse section through
a small portion of the cambium-ring
in a young black currant shoot, c Cam-
biurn ; a initial cell ; iv wood ; b bast;
/;/ medullary ray. ( Enlarged about 450
diameters )
ANNUAL-RINGS : KNOTS
123
present, and a similar addition is made to the bast on its inside.
The amount of wood produced by the cambium is always very
much greater than the bast. Moreover, the bast tissue consists
chiefly of thin-walled elements which become crushed into very
thin sheets by the pressure of the expanding wood and the re-
sistent bark, whereas the wood with its thick-walled cells and
vessels suffers little in this manner ; in transverse sections of the
a
FIG. 57.- i Piece of a stem of an ash tree A, Portion three
years old ; B, portion two years old. 2. Longitudinal and
transverse sections of same.
trunks and branches of trees and shrubs the cambium appears to
the naked eye to produce wood only.
(b) Annual rings : knots. If a tree is sawn across and the
cut surface then smoothed with a chisel a number of ring-like
zones are noticeable in the wood (Figs. 57 and 58); these are
124 ANATOMY OF STEM, ROOT AND LEAF
termed annual-rings and each represents the wood-tissue pro-
duced by the cambium during one active vegetative period.
From the beginning of one vegetative period to the commence-
ment of another is generally one year, so that in a two-year-old
stem two rings are visible, in one three-year-old three rings are
seen, and so on (Fig. 57).
It is on account of certain differences between the wood made
at the commencement of the growing season and that produced
at the end that we are able to recognise these successive yearly
additions to the wood as distinct bands, for if the structures pro-
duced by the cambium were of exactly similar character through-
out its life, it would not be possible to determine the points at
which the cambium had ceased or recommenced its growth.
When the cambium commences growth in spring it gives rise
to vessels and cells with thinner walls and wider cell-cavities
than those which it manufactures in late summer and autumn ;
in each annual ring (r, Fig. 64), therefore, two more or less
distinct portions are visible, namely, (i) a layer of spring-wood (s)
produced early in the growing season, and (ii) a layer of what is
termed autumn-wood (a) produced in late summer and autumn.
The spring-wood is generally of soft nature and pale colour ; in
oak, elm, ash, and Spanish chestnut its vessels are so wide that
they appear to the naked eye as a zone of pores.
The autumn-wood is harder and generally of darker colour ;
fewer vessels are present in it, and they are usually too small to
be seen with the naked eye.
The cambium of a stem is continuous with that of its
branches, and in a longitudinal section (Fig. 58) the annual
increment to the wood of the stem is seen to be continued in
the branches, although in the latter the amount added per
annum is smaller than in the stem, and consequently the annual
rings of a branch are narrower than those of same age in the
stem.
It will be seen from the above Fig. 5^ that the basal portions
ELEMENTS PRODUCED BY THE CAMBIUM 125
of a branch become buried by the wood added to the stem
year by year : on cutting a longitudinal board as indicated at
C, the buried part of the branch is cut almost transversely, and
appears as an oval knot (fc).
(c) Structures produced by the cambium : medullary rays.
As the cambium lies between the wood and bast, it is obvious that
the primary first-formed wood and bast of the vascular bundles
FIG. 58. A, Stem of a tree six years old with branch b ; B, longitudinal section of the
same, snowing all annual rings of stems except the first continued in branch; D } longi-
tudinal board cut from A; Xrknot (transverse section of branch b) ; / pith.
must be gradually pushed further apart by the secondary wood
and bast produced by the cambium, so that in old stems the
primary wood is found surrounding the pith in the centre,
while the primary bast is met with near the outside (<7, Fig. 60),
The structural elements forming the secondary wood are similar
126 ANATOMY OF STEM, ROOT AND LEAF
to those of the primary wood, namely, tracheae or vessels,
tracheids, fibres, fibrous cells and wood-parenchyma; the vessels
and tracheids, however, are never spirally or annularly thickened,
but usually marked with bordered pits and reticulate thickenings.
All these structures may be present or only a few; for
example, the wood of the yew consists of tracheids only, that of
the bulk of coniferous trees of tracheids and wood-parenchyma,
while the wocd of most dicotyledons contains all the above-
mentioned structures.
The elements of the secondary bast are similar to those of
the primary bast, namely, sieve-tubes with their companion-cells
and parenchyma; bast-fibres and living fibrous cells are also
present in some cases. After functioning for a short time as
conductors of food, the sieve-tubes, companion-cells and most of
the bast-parenchyma become empty, and in the older parts are
compressed into an irregular mass in which no cell cavities are
visible. When firm thick-walled bast-fibres are abundant, as
in lime and other trees, the bast in transverse sections appears
in the form of thin, ring-like bands.
Besides the production of wood and bast, certain cells of the
cambium-ring become changed into medullary ray cells (0,
Fig. 56); the primary medullary rays existing between the
first-formed vascular bundles of the unthickened stem are con-
tinued by the interfascicular cambium when thickening begins
and therefore always extend right through from the pith to
beyond the bast. Totally new secondary medullary rays are
subsequently started by certain cells of the cambium ring at
successive irregular intervals during the growth in thickness.
These new medullary rays extend from the annual rings of
wood in which they first appear to the corresponding bast
rings on the opposite side of the cambium ; they are therefore
of variable length.
The medullary rays are of variable width even in the same
stem. Sometimes they are only one cell thick and in trans-
HEART-WOOD AND SPLINT-WOOD 127
verse sections are scarcely visible to the naked eye, while in
oak, beech and other kinds of timber, many of them are several
cells thick, and in transverse sections appear as distinct light-
coloured radial bands (m t Fig. 64). In true radial longitudinal
sections, when seen at all, they appear as transverse bands of
variable vertical diameter running from the pith outwards
(Fig. 62), the primary rays have the greatest vertical breadth.
In longitudinal sections cut obliquely to the radius of the
stem small portions only are visible as bran-like spots.
The cells of the medullary rays are brick-shaped, generally with
thick pitted walls and living contents, which they often retain for
a long time. They conduct various food-products manufactured
in the leaves, and in winter starch and various food-substances
are stored in them for use in the following season. Air circulates
to all parts of the wood and bast in the intercellular spaces be-
tween the medullary ray cells.
(d) Heart-wood and splint-wood. In the old stems of oak,
walnut, larch, yew and other trees, the wood of the annual rings
in the centre of the tree is heavier, harder, darker in colour, and
drier than that of the younger rings near the cambium: this
dark wood is known as heart-wood or duramen^ while the light-
coloured softer wood surrounding it is termed splint-wood } sap-
wood or alburnum. The width of the splint-wood or the number
of annual rings over which it extends is not the same in all trees,
nor is it always the same in the same species of the same age.
The splint-wood is the part which conducts the * sap ' and many
of its parenchymatous cells are still living: starch, sugar and
other compounds readily attacked by fungi are generally stored in
it, and from its liability to rot it is valueless as timber.
The heart-wood acts as a strong support for the rest of the
tree : its vessels no longer conduct water and the parenchyma
of the wood and medullary rays have lost their living contents.
Various gummy and resinous compounds block up the cell-
cavities and in some cases calcium carbonate is present in
10
128 ANATOMY OF STEM, ROOT AND I EAF
them. Tyloses or peculiar bladder-like protrusions from the
adjoining thin-walled cells also block up the cavities of the
vessels. Tannin and colouring matters are also present in
the cell-membranes and cavities of the heart-wood of many trees.
Some of these substances act as preservatives against the attacks
of insects and fungi, and to them the durability of the heart-
wood is due. Whilst in oak, ash, elm, walnut, apple, laburnum,
larch, various pines, and many other trees a considerable
difference in colour is observable between the heart-wood and
splint-wood ; in beech, hornbeam, sycamore, lime, silver-fir, and
spruce no such distinction of colour is visible to the naked eye ;
but the heart-wood of these trees can frequently be distinguished
from the splint-wood by its dryness, although small numbers of
living cells are sometimes present in wood of this character right
through to the pith even in trees of considerable age. Trees of
the latter type are more liable to become hollow than those in
which a coloured heart-wood is present.
(e) Periderm. In annual
and perennial herbaceous
stems, the epidermis and
primary cortex grow at the
same time as the cambium
is increasing the bulk of wood
and bast in the vascular
cylinder, so that a continuous
covering is maintained in
such stems in spite of the
internal growth in thickness.
Even in some woody stems,
such as mistletoe and holly,
the epidermis persists and
keeps pace for years with the
growth of the wood and bast within. In the majority of woody
stems, however, the epidermis and primary cortex are ruptured
'hel-
FIG. 59. Transverse section throu
derm of a young black currant shoot,
logen ; c cork ; b phelloderm just forming J f
bast of the stem ; ^withered primary cortex ; t
epidermis. (Enlarged 270 diameters.)
PERIDERM 129
by the pressure exerted by the growth of the wood, and their place
is taken by totally new tissues which arise by division of a meristem
tissue known as the phellogen or cork-cambium (a, Fig. 59).
This phellogen may arise in the epidermis itself, in the cortex
or even in the pericycle within the vascular cylinder. The
divisions of its cells take place in a manner similar to those of
the ordinary cambium, but instead of producing wood and bast
tissue it gives rise on its inside to phelloderm or secondary cortical
tissue (b) and on its outside to cork (c). To the phellogen and
the products of its growth the term periderm is applied.
In most aerial stems little or no phelloderm is formed : when
present its cells have thin walls, and protoplasmic contents ;
chloroplasts are generally present in the tissue when it is
developed near the surface of the stem.
The cork-tissue formed by the phellogen shields and protects
the interior of the stem from mechanical injuries and prevents
the stem from losing water by transpiration.
Cork is also a bad conductor of heat and efficiently protects
the delicate phellogen and cambium from excessive heat in
summer and frost in winter.
It consists of a number of layers of cells which fit closely
together in regular radial rows (c). The cells soon die and
generally become rilled with air only ; their walls are mostly thin,
often brownish in colour and impermeable to water and gases.
' Corks ' for bottles are cut from the extensive cork-tissue of
the Cork Oak (Quercus Suber L.).
When the phellogen originates in a deep layer of cortical
cells or in the pericycle, all the tissues outside it become cut
off from water and food supply by the cork which is formed :
these tissues dry up in consequence, and, together with the
cork constitute what is sometimes spoken of as bark by botanists,
although in popular language the term bark is applied to all
tissues which are external to the cambium of a stem.
Scattered over the outer surface of the periderm of most woody
130 ANATOMY OF STEM, ROOT AND LEAF
branches and stems are small brownish or whitish spots termed
lenticcls\ they are well seen on stems of the elder, potato tubers, and
A B
C'
FIG. 60. Diagrams illustrating secondary growth in thickness of the stem of a dico
tyledon. A, A young stem before the formation of interfascicular cambium. J3, After inter-
fascicular cambium has formed. C, The same stem two years old. ( e Epidermis ; c cortex ;
it endoderrnis ; t pericycle ; w primary wood ; r cambium ; b primary bast of a vascular
bundle ; r 1 interfascicular cambium; / pith or medulla ; tn medullary rays; n phellogen ;
o cork ; c 1 secondary cortex ; x^ and x* annual rings of secondary wood ; f 1 and **
rings of secondary bast. ,
HEALING OF. WOUNDS ON WOODY STEMS 131
young apple and pear shoots. On ordinary shoots they are
developed at the places where stomata occur in the epidermis
and serve for the admission of air through the periderm into the
intercellular spaces of the medullary rays and other parts of the
stem.
(/) Healing of wounds on woody stems. Wounds made into
the soft parenchymatous parts of herbaceous stems, leaves, tubers,
FIG. 61. A, Stem with amputated branch (J) ; c callus.
B, Longitudinal section of A ; c callus formed by exposed cambium ; b exposed wood
of the branch.
C, Longitudinal section after the exposed wood of the branch has been completely
covered over by five annual growths ().
and fruits soon become healed over by the formation of a layer
of cork-cells which develop from the uninjured cells exposed
by the wound. When the mature wood of a stem or branch
is exposed (l>, Fig. 61) it becomes covered by the gradual
extension of a tissue manufactured chiefly by the cambium.
The cambium exposed ,by the cut and the very young cells of
the wood and bast at first give rise to a mass of soft parenchyma-
132 ANATOMY OF STEM, ROOT AND LEAF
tous tissue termed callus (c\ In the outer parts of the latter
there soon forms a cork-cambium while within it is developed
a new cambium from which wood and bast are ultimately pro-
duced. Year by year the new tissues produced by the cambium
extend further and further inwards over the exposed wood (b)
until the edges meet all round, after which time the cambium
exists as a continuous layer over the wounded surface (C 1 , Fig. 61).
The new wood formed as a cap-like covering over the exposed
old wood (<) does not actually coalesce with the latter and the
position of old wounds into the wood can always be easily
recognised in sections, although they may be so completely
overgrown and buried in the succeeding growth that no external
sign of their existence is visible.
The length of time necessary to cover a wound depends upon
its size, and the vigour and nutrition of the cambium. Clean
cut wounds heal more rapidly than jagged ones, and when large
branches are amputated with a saw it is advisable to trim the
exposed edges of the cambium with a sharp chisel or knife.
In the case of wounds where a considerable portion of old
wood is laid bare and which cannot therefore be overgrown
in a short time it is also important to cover this portion of
the wounded surface with Stockholm tar or some similar
antiseptic dressing to prevent its decay.
Ex. 69. Cut across one, two and three year old branches of ash, and
make the surface of the section smooth with a sharp knife : notice the annual
rings in each.
Make longitudinal sections of similar pieces of ash twigs, and notice the
arrangement of the yearly growths where one piece joins another a year
younger (compare with Fig. 57).
Make similar observations on as many common trees as possible.
Ex. 60. Prepare sections of a piece of a larch pole 4 or 5 inches in
diameter : cut with a saw and then carefully smooth with a sharp chisel or
plane.
Transverse, longitudinal, and oblique sections should be made.
Study the arrangement of the yearly rings in sections cut as in Fig. 58 to
illustrate the nature of a knot.
HEALING OF WOUNDS ON WOODY STEMS 133
Ex. 61. Examine boards of different kinds of wood : observe the arrange-
ment of the annual rings on the sides and ends. Try and determine whether
the boards were cut from near the middle or the outside of the trees.
Observe also the distribution and size of the knots.
Ex. 62. Cut blocks as in Fig. 62 of various kinds of common timber.
Examine with the naked eye and with a pocket lens : notice the presence
FIG. 62. Diagram showing transverse, radial, and tangential
views of a block of wood from a tree five years old. p Pith or
medulla; r' pnmaiy, r" secondly medullary rays; j zone of
porous spring- wood.
or absence of wide vessels in the spring zone of the annual ring, and the
number, width and other characters of the medullary rays as seen in transverse
and longitudinal sections.
Ex. 63. Notice the well-marked heart-wood in transverse sections of
larch, laburnum and other trees ; test whether the splint-wood is harder or
softer than the heart-wood.
Ex. 64. Notice the development of callus at the edge of the wound where
a thickish branch has been cut off an apple, pear or other tree.
Ex. 65. Make transverse sections through a young stem of a black
currant about mid-summer, mount them in a drop of water or glycerine.
Sketch the parts as seen with a low power ; afterwards use a high power,
and make drawings of small portions of the epidermis, cortex, cork, phellogen,
bast, cambium, wood pith and medullary rays.
134 ANATOMY OF STEM, ROOT AND LEAF
Cut longitudinal sections of the same j examine and make sketches of the
various parts.
Ex. 66. Cut and examine in a similar manner young one-year-old shoots
of beech, oak, elm and ash trees.
Also make and compare under a low power, transverse, radial and tan-
gential, longitudinal sections of pieces of the common timbers.
In the following tables are given the characters of the common
timbers, which can be easily distinguished with the naked eye
and a pocket lens :
I. TIMBER OF CONIFEROUS TREES.
In some of these timbers the annual rings are very distinct (Fig. 63), the
autumn- wood is hard and dark-brown or reddish in colour, and sharply
^^^^gjgmjimj^^^^ marked off from the spring-wood, which is soft and
^HHRHIRIHIH much paler in tint. Neither medullary rays nor
RRl^UliVflffflllffl porous rings arc visible.
WlffliltliHllHIM ' Heart-wood same colour as the Splint-wood.
(a) Silver Fir (Abies pectinata D. C.).
(b] Common Spruce (Picea excelsa Lk.).
Both these are soft 'white woods/ pale
yellowish or reddish-white in colour. The
spruce possesses a few fine resin ducts in
its autumn-wood which may be seen in
cross-sections as very small light spots :
they are missing from the wood of the
FIG. 63. Transverse sec- ., fi
tion through annual rings of silver nr.
larch timber. (Four times 2. Heart- wood in old dry timber, reddish-brown ;
natural si.) splint-wood, pale yellow.
(a) Larch (Larix europaa D. C.) Rings of autumn-wood dark red and
very distinct. The branches arise irregularly on the stem, so that
the knots on larch boards are scattered irregularly.
() Scots Pine (Finns sylvestris L.). Rings of autumn-wood not so
dark as larch, and contains larger, more distinct resin-ducts. The
branches arise in whorls at regular intervals, and the knots are
similarly distributed on boards cut irom this tree.
IL TIMBER OF DICOTYLEDONOUS TREES.
GROUP A.
Vessels of the spring- wood of each annual ring visible to the naked eye
as a distinct circle of pores (Fig. 64) ; autumn- wood denser.
TIMBER OF DICOTYLEDONOUS TREES 135
To this group belong :
Oak. Elm.
Ash. Spanish Chestnut.
I. Many medullary rays wide, and visible as light coloured radial bands.
Oak ( Quercus Robur L. ). (Fig. 64. )
Trt
FIG. 64. Transverse section through
annual rings of oak timber, r One annual
ring ; s spring-wood ; a autumn-wood ;
m broad medullary ray. (Four times
natural size.)
FIG. 65. Transverse section
through annual rings of ash. (Four
times natural size.)
FIG. 66. Transverse section FIG. 67. Transverse section
through annual rings of elm. through annual rings of Spani-h
(Four times natural size.) chestnut. (Four times natural
size.)
8. All medullary rays narrow, and fcarcely, or not at all, visible to the
naked eye.
(a) Asfc (Fraxinus excelsior L.). With a lens the fine vessels in the
autumn-wood appear few and scattered fairly regularly throughout.
(Fig. 65.)
136 ANATOMY OF STEM, ROOT AND LEAF
(#) Elm (Ulmus campestris Sm.). The fine vessels in the autumn-wood
appear arranged in many light coloured bands or lines more or less
parallel to the boundary of the annual ring (Fig. 66). The wood
of elm is darker than that of ash.
(c) Spanish Chestnut (Castanea vulgar is Lam.). The fine vessels of
the autumn-wood are arranged in radial lines (Fig. 67), dis-
tinguished from oak, which it somewhat resembles in colour, by
absence of wide medullary rays.
GROUP B.
Annual rings with little or no difference between the spring and autumn
portion ; vessels scarcely, or not at all, visible to the naked eye.
To this group belong :
Beech. Lime.
Hornbeam. Willow.
Sycamore. Poplar.
I. Some of the medullary rays broad and readily visible to the naked eye,
the rest fine and only seen with a lens.
(a) Beech (Fagits sylvatica L.). (Fig. 68.)
Wood reddish ; medullary rays with a
silky-shining lustre.
(/>) Hornbeam (Carpi >i us Betidus L.).
Wood yellowish- white ; medullary
rays dull and indistinct.
2. All the medullary rays very narrow, but
appearing to the naked eye as very fine distinct
lines.
(a) Sycamore (Acer Pseudo-plat anus L.).
Wood hard, heavy, and white or pale
yellow in colour.
(b) Lime (Ttlia Sp.). Wood light, soft,
and reddish-white.
3. Medullary rays quite invisible to the naked
eye.
(a) Willow (Salix caprea L.). Splint-
wood very pale red ; heart -wood deeper.
(b} Poplars (Populits Sp. ). Splint-wood white ; heart-wood brownish.
FIG. 68. Transvtrse section
through annual rings of beech.
(Four times natural size.)
C. Stems of Monocotyledons.
In transverse sections through the stem of a monocotyledon,
a conspicuous difference is seen in the arrangement of the
STEMS OF MONOCOTYLEDONS 137
vascular bundles from that met with in dicotyledons. Instead
of being arranged in a single ring, they appear scattered in
several irregular circles throughout the ground
tissue (Figs. 69 and 70). Usually the cortex is
very narrow and inconspicuous and a distinct pith
is rarely present. The bundles are common to
leaf and stem as in dicotyledons, but on entering
from a leaf they bend gradually inwards to near
the middle of the stem, and then generally curve
outwards again, finally joining other bundles
near the outside of the stem. vJsfs^uhTSgh
In addition to these differences, measurement JtemT^h^tSS
shows that the older parts of such stems which natural Mze ->
have ceased to grow in length are no thicker than the young parts
near the tip ; that is to say, the stems of most monocotyledons
do not increase in thickness when once they have ceased to grow
in length. This incapacity for growth in thickness is due to the
fact that the vascular bundles do not possess a cambium tissue, nor
is such meristem developed in the ground tissue except in a few
special cases which we cannot deal with here. Vascular bundles
in which no cambium is present are known as closed bundles.
In most grasses the vessels of the wood of each bundle are
few in number, and in transverse section appear arranged in
the form of a V (Figs. 70 and 71) ; the vessel nearest the centre
of the stem is annular, the others being spirally thickened.
Tracheids are not uncommon and thin-walled wood-parenchyma
is always present.
The bast which lies between the free limbs of the V-shaped
wood consists entirely of sieve-tubes and companion-cells.
The ground-tissue immediately surrounding each bundle is
generally thick-walled and gives mechanical support and pro-
tection to the soft parts of the bundle. Similar thickened ground-
tissue in larger or smaller amount is met with beneath the
epidermis, the rest being thin-walled tissue.
138 ANATOMY OF STEM, ROOT AND LEAF
Ex. 67. Cut sections through the stems of maize, asparagus, or any
species of lily : observe with a lens the scattered arrangement of the vascular
bundles.
Fio. 70. i. Transverse section through a barley stem, b Vascular bundles ; o ground"
tissue ; d hollow cavity. (Enlarged 14 diameters )
2. Enlarged view of portion A, a Thick-walled ground- tissue cells and epidermis;
o thin-walled ground-tissue cells ; b vascular bundle. (Enlarged about 90 diameters.)
o
Kxo. 7T. x. Transverse section of a. vascular bundle in
fca.rley stem. (Enlarged 4.20 diameters.)
a. Longitudinal section through portion ground- tissue
and a. vascular trundle along line _* in previous figure.
a. Epidermis and trtick.~\valled ground tissue cells ; o thin-
walle^l ground tissue cells ; s sieve- tube ; c companion-
cell of the bast; rt annular vessel; ft* and v" spiral
140 ANATOMY OF STEM, ROOT AND LEAF
Ex. 68. Make thin transverse sections of a wheat or barley stem. Ex-
amine with a low power : observe the thick walls of the epidermal and
subjacent ground-tissue cells ; note also the scattered vascular bundles and
hollow centre.
Sketch a single vascular bundle as seen under a high power ; note especially
the absence of cambium.
Take two or three pieces of barley or wheat straw each about a quarter of
an inch long, and press them flat. After placing them together, hold them
in your fingers and cut longitudinal sections, some of which will pass wholly
FIG. 72. i. Young
ot of a pea. // Root-
irs of the ptliferous
per ; c root-cap.
wice natural size. )
2. Transverse section through a young root of a pea near h in i.
h Root-hairs ; c cortex- , p piliferous layer : e endodermis : n pericycle ;
w wood strand ; .rits protoxylem ; b bast strand. (Enlarged 48 dia-
meters.)
or in part through a vascular bundle. Examine the sections first with a low
and then with a high power ; make sketches of the epidermis, thick and thin
walled ground-tissue, and annular or spiral vessels of the wood.
THE ROOT.
The outermost part of a young root, corresponding in position
with the epidermis of the stem, consists of a single layer of cells
THE ROOT 141
termed "the piliferous layer : it is directly concerned with the
important work of absorbing watery solutions from the soil. In
a transverse section (2, Fig. 72) taken at a point not far away
from the extreme end of the root, many of the cells of this layer
are seen to be much elongated ; these are the root-hairs^ pre-
viously mentioned in chapter iii. The cell-walls are all thin and
uncuticularised and are readily permeable to water, thus differing
essentially from the epidermal cells covering the parts above
ground.
Immediately beneath the piliferous layer is the cortex (c), which
is continuous with the same ground-tissue in the stem. The cells
of the cortex are usually parenchymatous and thin-walled with
many intercellular spaces between them; chloroplasts are fre-
quently absent, hence the pale colour of most young roots.
The innermost layer of the cortex, or the endodermis (*), is
generally very distinct in roots. Its cells are closely united with
each other in the form of an uninterrupted circle, an arrange-
ment which effectually prevents the leakage of gases from the
intercellular spaces of the cortex into the water-conducting tissues
of the central cylinder. The transference of water from the root-
hairs and cortex through the endodermis into the conducting
tissues of the central cylinder is, however, not interfered with.
In most roots the central cylinder is of smaller diameter, and
contains less parenchyma than that of the stem, although one is a
continuation of the other. It is, however, in the disposition of
the tissues within the central cylinder that the most important
differences between stems and roots are seen.
The pericycle (#), like that of a stem, may consist of a single
layer or several layers of cells. From this internal tissue arise all
lateral secondary roots, which must therefore necessarily bore
their way outwards through the surrounding cortex before they
become visible on the outside of the root (see Fig. 9). The
wood (w) and bast (ft) portions of the vascular bundles, instead
of being conjoined as in a stem, are arranged alternately side by
142 ANATOMY OF STEM, ROOT AND LEAF
side on separate radii drawn from the centre of the root with
small intervening bands of ground-tissue between them.
Moreover, in roots the first-formed, narrow-bored elements (x)
of the primary wood are nearest the outside, while in stems they
are nearest the centre.
According as the number of separate strands of wood is two,
three, or many, the roots are described as diarch, triarch (as in
Fig. 72), <x poly arch respectively.
The number of rows of secondary roots generally corresponds
to the number of strands of primary wood in the parent root,
each row being formed in the pericycle almost opposite a wood
strand.
In all roots the development of the primary wood proceeds in-
wards and frequently it goes on until the several strands unite to
form a mass which occupies the centre to the complete exclusion
of pith. Nevertheless, in some roots, and especially those of
monocotyledonous plants, pith is present.
The roots of perennial dicotyledons increase in thickness
just as the stems do, but owing to the different disposition of
the primary tissues the first formation of the cambium is not
the same as in a stem. In roots the cambium first forms in
the ground-tissue on the inside of the bast-strands, and sub-
sequently within the pericycle opposite the primary wood ; in
transverse sections, therefore, the cambium in the early stages of
its existence appears as a wavy band of meristem (2, <:, Fig. 73).
When active growth of the cambium takes place, the wavy
outline is soon lost and it is then seen as a simple ring of
meristem, producing secondary wood and bast in a manner
precisely similar to the cambium of an ordinary stem.
In roots which grow in thickness, a phellogen arises in the
pericycle and like that of thickening stems produces cork ex-
ternally and phelloderm internally. In consequence of the
formation of a ring of cork by the phellogen, all the tissues
external to it, namely, the endodermis, primary cortex and
THE ROOT
143
piliferous layer, wither and shrivel. The older portions of a
root after becoming covered by a protective periderm lose
their absorptive function and henceforward act chiefly as con-
ductors of the watery solutions absorbed by the younger parts
still possessing root-hairs. For an account of the characteristic
root-cap which covers the growing point of practically all roots
see pp. 149 and 150.
1 2
s
FIG. 73. Diagram illustrating secondary growth in thickness of
the root of a dicotyledon, i. Transverse section of a very young
root. 2. The same after the cambium (c) has formed a continuous
band. ^. The same after secondary thickening has been in progress
some time. / Piliferous layer ; * primary cortex ; e endodermis ;
*pericycle; b' primary bast; w' primary wood; c cambium;
b " secondary bast ; w " secondary wood ; r secondary cortex
in primary medullary ray.
Ex. 69. Soak some peas and barley grains in water for six or seven
hours, and afterwards allow them to germinate on damp blotting paper or
flannel as in Ex. 3. When the root-hairs are visible on the young roots
examine them with a lens and make sketches noting especially their origin
away from the extreme tip.
Strip off with forceps a piece of the outer portion of a root, so as to
II
144 ANATOMY OF STEM, ROOT AND LEAF
include the root-hairs : mount it in water and examine first with a low and
then with a high power.
Ex. 70. Cut transverse sections of a young root of a bean or pea through
the region bearing root-hairs, and place them for twenty minutes in ' Eau
de Javelle ' (Ex. 75) : wash them and mount in glycerine.
Examine with a low power ; observe and sketch the piliferous layer bear-
ing root-hairs, the parenchymatous cortex and the central vascular cylinder.
Examine with a high power and make drawings of the wood and bast
strands, pericycle and endodermis.
Ex. 71. Cut transverse sections of the older parts of the root of a pea or
bean, near where the lateral roots are just beginning to appear. Clear with
*Eau de Javelle' and mount in glycerine. Make a sketch of a section
which shows the lateral roots boring their way through the cortex.
THE GEEEN FOLIAGE-LEAP.
The leaves are built up of the same tissues as the stems and
roots, namely, of epidermis, vascular bundles, and ground-tissue,
but the arrangement and constitution of these tissues are different.
The vascular bundles coming from the stem run into the leaf
and in dicotyledons branch repeatedly in one plane to form a fine
net-work of strands, which conducts sap to and from all parts of
the leaf and at the same time acts as a firm framework for
the support of the soft ground-tissue. In monocotyledons the
main branches of the bundles which enter a leaf generally take
a parallel course and are connected by smaller oblique strands.
The bundles of the leaves are always closed, there being no
need for an active cambium in parts of the plant which are of
such limited growth.
As the bundles curve out of the stem into the leaf without
twisting, the wood comes to lie nearest the upper surface of the
leaf, and the bast nearest the lower surface.
With the exception of the absence of cambium the larger
vascular bundles of the leaf resemble those of the stem. The
wood of the finer strands, however, consists of spirally thickened
elements only, and the extreme tips of the bundles which in
THE GREEN FOLIAGE-LEAF 145
dicotyledons end blindly among the ground-tissue cells, are
formed entirely of tracheids.
The bast-tissue also undergoes a reduction of elements : as
the end of the bundle is approached, the sieve-tubes and com-
panion-cells are replaced by single long cells which do not extend
so far as the woody elements of the bundle. Surrounding
each bundle of the leaf is a sheathing tissue of parenchyma
which is continuous with the parenchyma of the vascular
cylinder of the stem. Such bundle-sheaths conduct carbohydrates
from the leaf to the stem and frequently contain small starch-
grains.
The epidermis covers the whole leaf and, like that of the
stem with which it is continuous, consists of a single layer of
cells, the outer walls of which have a protective cuticle.
A surface view (Fig. 74) shows that the cells fit closely
together except where the stomata occur. Each stoma consists
of two curved sausage-shaped cells (a) termed guard-cells, which
are joined together at the ends in such a manner that a narrow
slit-like pore or opening is left between them. The pore leads
through the epidermis into a
somewhat large air-chamber
just inside the ground-tissue
of the leaf, and this chamber
communicates with the air-
filled intercellular spaces all
through the leaf.
Changes in the curvature
of the guard-cells reduce
or increase the size of the -/ P ^ f == ^^^/\J U
pores of the stomata ; when
., n i j FIG. 74. Surface view of the epidermis of
the Cells are mUCh Curved ? bean leaf, a Guard-cells of a stoma;<nheopen-
the pore is widely opened ing between them ' (Enlarged 32 diameters ->
and when they become straight the slit is closed.
The stomata are organs specially adapted for the escape of
146 ANATOMY OF STEM, ROOT AND LEAF
water-vapour in the transpiration process, and are concerned
also with the interchange of gases which goes on between the
atmosphere and the air within the plant in the process of
respiration and 'assimilation.'
FIG. 75.--I. Transverse section through a plum leaf (somewhat diagrammatic).
2. Enlarged view of portion A from i. * Epidermis ; x stomata ; p palisade parenchyma J
s spongy parenchyma ; b vascular bundles. (Enlarged 160 diameters.)
The ground-tissue of the leaf is a continuation of the cortex
of the stem and is termed the mesophylL In ordinary flat leaves
THE GREEN FOLIAGE-LEAF 147
it is generally differentiated into two distinct parts, namely,
(i) the palisade parenchyma which lies beneath the upper
epidermis of the leaf, and (ii) the spongy parenchyma which
extends between (i) and the lower epidermis. A transverse
section across a leaf is given in Fig. 75. The cells forming
the palisade tissue are somewhat cylindrical with their long cells
at right angles to the surface of the leaf; they have very few
intercellular spaces between them. The cells of the spongy
parenchyma are very irregular in form and enclose large inter-
cellular spaces.
All the cells of the mesophyll contain numerous chloroplasts
but it is in the palisade cells that they are most abundant, a
fact which, together with the comparative absence of intercellular
spaces, accounts for the upper side of a leaf being usually a
deeper green colour than the lower side.
Ex. 72. Strip off a piece of the lower epidermis of a bean leaf and mount
it in water. Note the irregular outline of the cell-walls and the way in which
they fit one with another. Make sketches of these and of the stomata with
their guard-cells. Examine, in a similar way, the upper and lower epidermis
of the leaves of turnip, plum, apple, onion, grasses and other common plants.
Note the form of any hairs which are present.
Ex. 73. Cut five or six pieces, each about one-eighth of an inch broad
and half an inch long, from the blades of a plum leaf. Place them one on
another, hold them in the fingers and cut transverse sections. Mount some
of the thinnest sections in water and examine first with a low and then with
a high power.
Sketch the parts seen, namely,
(1) The upper and lower epidermis with nuclei, protoplasm, and clear
cell-sap ;
(2) The palisade tissue of several layers ; and
(3) The spongy parenchyma in which are many large intercellular spaces.
Possibly the sections of one or more stomata may be seen.
Ex. 74. Cut transverse sections through the mid-rib and petiole of several
different kinds of leaves. Note and sketch the position and character of the
wood and bast of the vascular bundles cut across ; and also the thickness
of the walls and nature of the contents of the cells surrounding the bundles.
Ex. 75. Prepare some * Eau de Javelle ' by first dissolving two ounces of
carbonate of soda in a pint of water and then adding one ounce of * bleaching
148 ANATOMY OF STEM, ROOT AND LEAF
powder.' Allow the mixture to stand after stirring, and pour off the clear
liquid into a well-stoppered glass bottle: keep in the dark.
Collect a few thin leaves of plants and kill them by immersing them for a
minute in boiling water. Then place them in some ' Eau de Javelle ' ;
leave them in it a few hours and when quite bleached, wash in water for
an hour or two and then mount in weak glycerine. Examine with a low
power, observe the ramifications and endings of the bundles, also the parcn-
chymatous bundle-sheath. Focus on the surface and note the form, number,
and size of the stomata and hairs.
FIG. 76. Diagrammatic longi-
tudinal section through the apex of a
stem, d Dermatogen which gives rise
to the epidermis e \ c cortex produced
from pcnhlem a ; s vascular cylinder
produced from plerome b ; / leaves.
FIG. 77. Enlarged view of the apex of
the stem in the previous figure, d Derma-
togen ; a periblem ; b plerome ; v vessels
of the protoxylem ; /rudimentary leaves.
THE GROWING-POINTS OF STEMS AND BOOTS.
The growing-points or regions where the formation of new
organs and tissues takes place are situated at the end of the
stems and roots.
(i) Growing-point of the stem. The apex of the stem is
GROWING-POINTS OF STEMS AND ROOTS 149
always completely enclosed and protected by young leaves
(Fig. 76) and consists of a dome-shaped mass of meristem,
from which are derived all the various tissues already studied in
the mature stem and leaf. The cells forming the meristem, are
approximately uniform in size and form : they possess thin walls
and are rich in protoplasm.
In a favourable longitudinal section through the growing-point
three distinct strata are often visible (Figs. 76 and 77). Covering
the apex is a single layer (d) termed the dermatogen which divides
only by walls at right angles to the surface and gives rise to the
epidermis of the plant.
Beneath the dermatogen comes the periblem (a) from which
the cortex is derived. At the extreme apex it may be only one
cell thick, but in the older parts division takes place in several
directions and a many-layered stratum is produced.
Occupying the centre is a solid mass of meristem termed the
pkrome (b): from it the vascular cylinder is developed within
which at a short distance from the apex the differentiation of the
vascular bundles begins to appear.
The leaves of the plant are first seen as slight projections (/)
on the surface of the growing-point ; the tissues taking part in
their formation are the dermatogen and a portion of the periblem.
The branches which arise in the axils of the leaves are also
developed from the dermatogen and periblem ; the plerome
is not concerned in the production of either leaves or
branches.
(ii) Growing-point of the root. The apex of a root differs very
considerably from that of a stem. The delicate meristem in the
latter always exists within a bud and is protected from external
injurious influences by the rudimentary leaves which curve
round it.
Roots, however, produce no leaves, but the tender cells of the
meristem at the apex of each are protected by a covering of
cells termed the root-cap. Moreover, as fast as the exterior of
150 ANATOMY OF STEM, ROOT AND LEAF
the root-cap dies off or is worn away by the soil in which the
root is growing, additions are being made to the interior of the
cap where it is in union with the meristem.
A common arrangement of the tissues at the end of a root
is seen in Fig. 78.
The innermost part of the
meristem which gives rise to the
vascular cylinder is the plerome
(), while round it is the peri-
blem (#), from which the primary
cortex of the root is derived.
In almost all respects these
portions of the apical meristem
are identical with those present
in the apex of the stem. The
outermost part of the meristem
is termed the calyptrogen or cap-
forming layer; instead of re-
maining a single layer as in the
stem it divides by walls parallel
to the surface as well as per-
pendicular to the latter, and thus
a many-layered root-cap (c) is
formed.
In many instances the inner-
most single layer of cells pro-
J
FIG. 78. Longitudinal section through
the apex of a root, b Plerome ; a penblem ;
c root-cap ; d external dead and dying cells
of root-cap ; e pericycle ; v vessels of the
(EnJ " gcdab ut duced by the" calyptrogen "be-
comes the piliferous layer : the rest of the cells which are
continually cut off towards the outside form the root-cap
proper.
Ex. 76. Soak some beans or peas, and allow them to germinate. As
soon as the tip of the radicle is visible through the micropyle, strip off the
coat of the seed and cut longitudinal sections of the young root. Place them
for half an hour in Eau de Javelle (see Ex. 75), then wash in water and
GROWING-POINTS OF STEMS AND ROOTS 151
mount in dilute glycerine. Examine first with low and then with a high
power. Make a sketch showing the general arrangements of the parts
seen, viz., root-cap, plerome and periblem.
Endeavour to prepare sections of the apex of the roots of maize, peas, and
other large seeds.
Ex. 77. Cut longitudinal sections through the apex of stems within the
terminal buds of common trees. Treat and examine as indicated above.
Observe and sketch the parts seen : note the first beginnings of leaves.
PART III.
PHYSIOLOGY OF PLANTS.
CHAPTER XL
THE CHEMICAL COMPOSITION OP PLANTS.
t. AFTER becoming acquainted with the external and internal
structure of plants, it is necessary to proceed to study the work
which the various parts perform in the maintenance of the life of
the plant : this branch of the science of Botany is termed physi-
ology. Among the higher forms of plants various members and
tissues are adapted to carry out certain functions or certain kinds
of physiological work ; the individual members and tissues by
which the functions are performed being termed organs of the
plant.
It is at the outset important to emphasise the fact that all the
various functions are dependent upon the living protoplasm, and
that the activity and power of the latter to carry them on satis-
factorily is bound up with certain external conditions, namely, a
suitable temperature, adequate supply of food-materials, and in
the case of green plants a certain intensity of light, and access to
free oxygen of the atmosphere; without the fulfilment of these
conditions death takes place and the various vital phenomena
cease.
The functions of plants may be divided into two groups :
(i) The nutritive functions which are concerned with the
absorption, elaboration, and appropriation of the food-supply
and therefore specially adapted to the maintenance of the life of
the individual,
152
CHEMICAL COMPOSITION OF PLANTS 153
and (ii) the reproductive functions concerned with the produc-
tion of new individuals and the maintenance of the species.
2. Before examining the nutritive processes in detail, it is
necessary to learn something about the substances entering into
the composition of plants.
If a fresh plant is dug up from the ground and placed in an
oven heated to a temperature a little above that of boiling water
(105- 1 10* C.) it soon loses weight, the loss being due to the
escape of water from the tissues of the plant. By continuing the
drying process for some hours, all the water from the cell-sap,
protoplasm, and the cell-walls is expelled, and there remains
only the solid matter of the plant.
This residue or dry matter consists of a great variety of
chemical compounds, organic and inorganic ; when ignited and
burnt it always leaves a small amount of white or yellowish
incombustible ash, composed of inorganic compounds, the chief
constituents of which have been originally absorbed from the
soil by the roots of the plant.
The following table shows the amounts of water, dry matter,
and ash in 100 parts by weight of the seeds, fruits, leaves, and
other portions of a few common plants :
Water.
Wheat (grain),
14*3
Barley .
14*3
Oat .
14-3
Beans, .
15-0
Turnip-seeds,
n-8
Apples,
84-8
Roots of Carrot,
85-0
Swede, .
87-0
Mangel, .
88-0
Potato tubers, .
75'
Good dry hay,
'4*3
loiai
dry
matter.
Combustible
portion.
Ash.
857
76-5
9*2
857
727
13*0
857
757
ro'o
85-0
79*5
5*5
88-2
84-3
3*9
*S'*
14-8
0*4
J 5'
14-1
0-9
13-0
1 2*0
I'O
12'0
n'2
0-8
25'0
24-1
0*9
857
79*5
6'2
154 CHEMICAL COMPOSITION OF PLANTS
Meadow grass (green), 80*0 20*0 18*0 2*0
Red Clover, . . 80-4 19*6 18-3 1*3
Green potato haulm, 85*0 15-0 13-4 i'6
Swede leaves, . 88*4 11*6 9*3 2*3
Mangel leaves, 90*5 9*5 77 1*8
The amount of water in ripe seeds is comparatively small,
generally averaging from 10 to 15 per cent. In succulent fruits,
fleshy roots, tubers, green leaves and fresh vegetative organs, it
is rarely less than 75 per cent, and not unfrequently as high as
85 to 90 per cent, of their total weight.
The proportion of ash in the dry matter of seeds and succulent
roots and tubers is generally very much smaller than in the
leaves and bark of plants.
Ex. 78. Weigh pieces of carrot, turnip, mangel, potato, apple and
strawberry in separate porcelain dishes, then cut each piece into several small
pieces and place the porcelain dishes and contents in a warm oven or ' water-
oven. ' Weigh at intervals of three hours and note the loss in weight.
Ex. 79. Repeat the previous experiment with leaves of potato, turnip,
ash and other trees, freshly-cut grass, and freshly-ground ' whole-meal '
flour, oat-meal and bean-meal.
3. The dry matter of a plant consists of (i) a small amount of
unutilised inorganic substances absorbed from the soil ; and (2)
a large amount of various organic compounds manufactured by
the plant out of the food-materials which it has absorbed from
the soil and air.
To merely give a list of the compounds met with in plants
would fill a large volume : it is, however, not needful here to
describe more than the chief organic substances of which the
plant-body is composed : for present purposes they may be
classified into two groups, namely : ( i ) non-nitrogtnous and
(2) nitrogenous substances according as they are free from 01
contain nitrogen.
CARBOHYDRATES 155
I. NON-NITROGENOUS ORGANIC SUBSTANCES.
The most important members of this group are the carbo-
hydrates, fats, oils and acids enumerated below.
i. Carbohydrates. These compounds form the largest part
of the body of all plants and contain carbon, hydrogen and
oxygen, the elements hydrogen and oxygen being present in the
same proportion as they exist in water. The chief carbohydrates
are the sugars, starch, inulin, celluloses and pentosans.
a. Sugars. Almost all the sugars possess a more or less
sweet taste, and are generally met with dissolved in the cell-sap.
The commoner representatives are glucose, fructose, cane-sugar
and maltose.
(i) Glucose, dextrose or grape-sugar (C 6 H 12 O 6 ), occurs in most
fruits, and especially in grapes whose cell-sap may contain from
20 to 30 per cent. ; ripe apples contain on an average 7 to 10
per cent. ; cherries 9 to 10 per cent., and plums 3 to 5 per cent
of this sugar.
(ii) Fructose Jruit-sugar, or levulose (C 6 H 12 6 ) is found also in
ripe fruits associated with grape-sugar.
Both dextrose and levulose reduce Fehling's solution, and are
directly fermentable by yeast.
Ex. 80. Dissolve 35 grams of copper sulphate in 500 c.c. of water, label
this solution A : then dissolve 160 grams of caustic potash and 173 grams of
sodium potassium tartrate in 500 c.c. of water and label the solution B. By
mixing equal quantities of A and B, Fehling's solution is produced. (The
solution A and B should be kept separate and only mixed when needed as
the mixture does not keep long. )
Squeeze a few drops of grape juice into a test tube containing 10 c.c. of the
Fehling's solution : heat over a Bunsen flame and note the reddish precipitate
of cuprous oxide (Cu*O).
Test the juice of ripe plums and other fruits in the same way.
(iii) Cane-sugar or saccharose (C^H^On) occurs dissolved in
the cell-sap of the stems and roots of many plants and especially in
the sugar-cane, mangel and sugar-beet, from which it is extracted
on a commercial scale.
156 CHEMICAL COMPOSITION OF PLANTS
Sugar-cane stems contain from 1 5 to 20 per cent., the sugar-
beet from 12 to 1 6 per cent, of this carbohydrate.
It differs from the two previous sugars in that it does not
reduce Fehling's solution and cannot be fermented directly by
yeast. When boiled with dilute acids or acted upon by the
enzyme invert ase^ which is present in yeast and in various
tissues of plants, it decomposes into a mixture of dextrose and
levulose which mixture is termed invert-sugar,
Ex. 81. Boil some pieces of mangel or sugar-beet in water and
(i) Test some of the solution for a * reducing ' sugar as in Ex. 80.
(ii) Take 10 c.c. of the solution and add to it three or four drops of strong
hydrochloric acid : boil for twenty minutes, and after neutralising the acid
with a solution of sodium carbonate, boil and test again with Fehling's
solutions.
(iv) Maltose (C 12 H 22 O n ) is a variety of sugar formed by the
action of the enzyme diastase upon starch and is present in
malted barley and other germinated grain. It is capable of
direct fermentation by yeast, and reduces Fehling's solution but
not to the same extent as grape-sugar.
b. Starch (C 6 H 10 O 6 ) n . This carbohydrate is found in the
form of minute solid, organised grains, built up of several
successive layers of the substance arranged round a more or
less central nucleus or hilum\ sometimes two or more nuclei
are visible in the same grain in which case the latter is described
as compound.
Starch-grains are usually manufactured by the plastids of the
cells, and occur in greatest abundance in roots, tubers and seeds
where they form a store of reserve-food : from 50 to 70 per
cent of the dry weight of cereal grains, and 10 to 30 per cent,
of potatoes is starch.
The grains are variable in size and form even in the same
plant : nevertheless, in many cases the starch-grains from certain
plants are so characteristic in shape and dimensions that they
may be readily identified under the microscope.
CARBOHYDRATES
157
Those from potato tubers are flattened irregularly oval grains
of comparatively large size, with an excentric nucleus (i, Fig. 79).
Large and small grains are present in the endosperm-cells of
wheat, barley and rye ; they are all flattened and lentil-shaped
with a central nucleus (2, Fig. 79).
In the cotyledons of the seeds of pea, bean and other legu-
minous plants, the grains are oval and kidney-shaped as in 4,
Fig. 79, with radiating cracks or fissures in the centre.
In oats the grains are oval and compound (3, Fig. 79), the
component fragments (;/) being small and angular.
FIG. 79. (i) Starch-grains of potato : n nucleus of a grain, (a)
Starch-grains of wheat. (3) Siarch-grains of oat ; a a compound
gram ; n fragments of a compound grain. (4) Starch-grains of bean.
(All enlarged 360 diameters.)
158 CHEMICAL COMPOSITION OF PLANTS
The substance forming the grain is termed starch or amylose,
of which there appears to be two slightly different modifications.
When treated with a solution of iodine it turns a characteristic
deep violet-blue colour.
The enzyme diastase converts it into maltose and various
soluble gum-like carbohydrates termed dextrins.
Formerly Nageli and others considered that a starch-grain
consisted of two substances, namely, granulose^ and a substance
starch-cellulose or farinose which remains as an insoluble residue
when starch-grains are treated with saliva or weak acids : this
residue, however, does not pre-exist in the starch-grains but is
a product of the action of the solvents employed, and according
to A. Meyer is amylodextrin.
On boiling with dilute acids starch is changed into glucose
and dextrin.
Heated with water starch swells and forms an insoluble jelly-
like paste : subjected to dry heat or roasted to a temperature of
150 to 200 C. it turns brown and becomes altered into a form
of dextrin.
In certain cases starch-grains contain amylose with a larger or
smaller proportion of amylodextrin : the latter is coloured wine-
red by a solution of iodine.
Commercial starch is obtained chiefly by mechanical separation
with water from crushed potato tubers, or from maize and wheat
grains.
Ex. 82. Divide a grain of wheat, barley, oat, rye, maize and rice trans-
versely with a knife. Gently scrape off a very small portion of the endosperm
and mount in water. Examine the starch-grains with a low and a high
power, noting whether simple compound, their form and relative size, and
also the shape and position of the hilum in each.
Ex. 83. Cut through the cotyledons of a bean and pea seed and also
through a potato tuber : gently scrape the cut surface with the point of a knife
and transfer the starch -grains obtained to a drop of water on a slide. Examine
and note the form, size and shape of the starch-grains.
Ex. 84. Cut thin sections from a piece of potato tuber and from a wheat
CARBOHYDRATES 159
grain : examine with a low power and make drawings of the starch-grains
within the cells observed.
Ex. 85. Make a strong solution of potassium iodide in water and add to
it a few crystals of iodine. Allow the mixture to stand for twelve hours, and
shake occasionally in order to facilitate the solution of the iodine. When the
latter is all dissolved, add more water until the whole is the colour of dark
sherry.
When examining the starch-grains in Exs. 82 to 84, place a drop of this
solution near the edge of the cover -slip so that it may run under the latter
and come in contact with the starch-grains. Note the change in colour of the
starch-grains.
Ex. 86. Make an extract of malt diastase as follows : Shake up five grains
of ground malt with 50 c.c. of cold water and after allowing it to stand for
four hours, filter so as to get a clear solution.
Next grind some starch with water in a mortar and pour a little of the
mixture into a 200 c.c. flask of boiling water. When cool pour about 20 c.c.
of this thin starch paste into three test tubes : show the presence of starch by
adding a few drops of the solution of iodine mentioned in Ex. 85 to one
tube, and to the other two tubes add 3 or 4 c.c. of the diastase extract, and
warm them to 60 C. Test for the presence of starch in one of these two tubes
by taking out at intervals of five minutes a few drops with a pipette and adding
them to weak solutions of iodine kept in a series of test tubes.
After a time the starch is changed into sugar and dextrin : When this has
happened show the presence of the sugar by means of Fehling's solution.
See if Fehling's solution is acted upon by the thin starch- paste when no
diastase is added.
c. Celluloses. The solid fabric of a plant consists mainly of
cell-walls which are produced by the protoplasm of the cells.
At first the walls are thin, but in many cases thickening takes
place by the deposition of layer after layer of sybstance on the
inside of the walls where they are in contact with the cytoplasm.
Where cells are in a state of division and new walls are being
produced, the latter are first visible in the form of thin plates of
cytoplasmic substance stretched across the dividing cells, and in
the process of thickening the new layers appear to be produced
by a conversion of the outermost layers of the cytoplasm, for
where thickening of a cell-wall takes place there is always noticed
a gradual diminution of the protoplasmic cell-contents until at
last none remain within the cell-cavity.
12
i6o CHEMICAL COMPOSITION OF PLANTS
It has been customary to term the material forming the cell-
wall cellulose, as if it were a single chemical substance. A
variety of celluloses are, however, now known and the cell-walls
of plants invariably consist of mixtures or compounds of these
with several other substances.
What may be named the typical cellulose can be readily
obtained from cotton-wool and flax-fibre by treating the latter
with various chemical reagents to eliminate the substances com-
bined or mixed with it : it is a carbohydrate possessing the
empirical composition represented by the formula (C 6 H 10 O 5 ) B .
This typical cellulose is insoluble in dilute acids and alkalies,
but is soluble in ammoniacal cupric oxide, hot concentrated
solutions of zinc chloride and other solvents.
It stains blue when treated with sulphuric acid and iodine or
with * chlor-zinc-iodine,' and when acted upon with concentrated
sulphuric acid yields dextrose sugar.
Another type of cellulose is present in the cell-walls of
lignified tissues. When obtained free from the substances with
which they are combined or mixed, these celluloses differ from
the cellulose obtained from cotton fibre not so much in empirical
composition as in chemical structure. They contain a slightly
higher percentage of oxygen, are less resistant to hydrolysis, and
yield only small quantities of dextrose and mannose sugars when
treated with sulphuric acid ; moreover the aldehyde furfural is
produced when celluloses of this type are hydrolysed with dilute
hydrochloric acid.
The cell-walls of the cells of the endosperm-tissue and coty-
ledons of seeds are formed of substances termed hemicelluloses,
which are so different in chemical properties from the two types
just mentioned that they have little right to be considered cellu-
loses at all, except that . they resemble the latter in appearance
and are the materials of which certain cell-walls are composed.
Hetnicelluloses are very easily hydrolysed by dilute acids and
alkalies into galactose, mannose and pentose sugars.
CARBOHYDRATES 161
None of the above-mentioned celluloses are ever met with in
a pure state in plants ; they are always combined or mixed with
other substances forming three main types of what may be termed
compound celluloses as indicated below.
(i) Pectocelluloses. These are compounds or intimate mixtures
of typical celluloses with pectose \ the latter when hydrolysed with
dilute acids or alkalies yields pectin, a substance whose solutions
gelatinise easily. The cell-walls of raw cotton, flax-fibres and
other unlignified fibres, as well as most parenchymatous tissues
and especially those of fleshy roots and fruits, such as carrots,
mangel, turnips, apples, pears and currants, consist chiefly of
this form of compound cellulose.
Mangin asserts that the first walls produced during cell-division,
consist mainly of pectose, the secondary thickening-layers of
most unlignified cell-walls being formed of cellulose and pectose
combined.
Closely allied to pectocelluloses are the mucocelluloses composed
of cellulose and substances which yield mucilaginous solutions with
water : they are chiefly met with in certain seeds and fruits.
(ii) Adipocelluloses. The cell- walls of cork-tissue appear to be
composed chiefly of a fatty or waxy substance termed suberin
combined with a very small amount of cellulose. Allied to these
are the cutocelluloses forming the cell-walls of the epidermis of
plants : the substance eutin closely resembles suberin in its
composition and properties. Both suberised and cutinised cell-
walls turn brownish-yellow when treated with ' chlor-zinc-iodine ' ;
they are impermeable to water and successfully prevent the loss
of water from tissues covered by them. Whether cutin and
suberin are products of the direct conversion of cellulose is a
question at present unsolved.
(iii) Li%nocelluloses. The cell-walls of the woody tissues of
plants consist vi lignocelluloses which are homogeneous compounds
of (a) cellulose or oxycellulose,
(&) a pentosan known as wood-gum,
162 CHEMICAL COMPOSITION OF PLANTS
and (f) certain aromatic compounds not yet isolated in a pure
state : the substances b and c are together generally spoken of as
lignin or lignonc. Lignocellu loses are primary constituents of
plant tissues, and are not celluloses on which c lignin ' is encrusted
or deposited as the result of secondary chemical changes.
Lignified walls become pink when treated with phloroglucin
and hydrochloric acid, and stain a yellow colour in solutions of
aniline chloride ; with chlor-zinc-iodine the walls become yellow.
The cell-walls of lignified tissues in the heart-wood of trees,
and other parts of plants, frequently become stained by tannin
and various colouring matters.
Paper of all kinds consists chiefly of cellulose obtained from
linen rags, cotton, wood and straw.
Ex. 87. To prepare ' chlor-zinc-iodine,' dissolve 25 parts of zinc chloride
and 8 parts of potassium iodide in 8J parts of water, and add as much iodine
as will make the solution a dark sherry colour.
Cut sections of the stems and other parts of plants, and mount them in the
solution ; note the blue colour of the unlignified and uncuticularised walls-
Notice the effect of the solution upon ' cotton-wool/ and upon sections of wood
Ex. 88. Cut sections of the seeds with a dry razor ; mount and examine
some of the sections in water, and some in pure glycerine. Soak some white
mustard and flax-seeds (linseed) in water ; note the slimy mucilaginous nature
of the surface of the seeds when wetted.
Ex. 89. Cut sections of the stems of various plants, and mount them in a
saturated solution of aniline chloride, to which a few drops of hydrochloric
acid have been added ; the lignified walls stain a golden yellow colour.
d. Pentosans. Associated with the cellulose of plant tissues
are carbohydrates termed pcntosans (C B H 8 O 4 ). When heated
with dilute acids they are hydrolysed and converted into the
pentose sugars (C 5 H 10 O 5 ) arabinose or xylose.
Pentosans are produced during the early stage of growth, and
the amount generally increases with the age of the plant.
These carbohydrates appear to be of little use in the nutritive
processes of plants, but are partially digested and assimilated by
herbivorous animals, They are common in all plant tissues and
are especially abundant in grasses and cereal straw.
FATS AND FIXED OILS 163
e. Inulin is a carbohydrate possessing the same percentage
composition as starch ; it is soluble in water, and is met with dis-
solved in the cell-sap of many plants belonging to the Composite,
Campanulaceae and other orders. It is also found in the bulbs
of many plants belonging to the Liliaceae and Amaryllidaceae, as
well as in the leaves and other vegetative parts of these plants.
Inulin is especially abundant in dahlia and chicory roots, and
in tubers of Jerusalem artichoke, where it takes the place of starch
as a reserve-food. When portions of these roots and tubers are
placed in dilute alcohol for several days, the inulin separates in
the form of solid spherical masses of needle-like crystals, arranged
in a characteristic radiated manner (sphaerites).
Inulin does not reduce Fehling's solution, but when boiled for
a long time with water, or for a short time with dilute acids, it is
converted completely into levulose.
Ex. 90. Soak a piece of a dahlia root in strong methylated spirit for several
weeks : cut sections and mount in pure glycerine. Examine and draw the
sphaerocrystals of inulin.
2. Fats and fixed oils. These substances, which are mixtures
of different compounds of glycerine and fatty acids, contain the
same three elements as the carbohydrates, but possess less oxygen
proportionately to hydrogen than the latter substances. They
are at first most frequently observed in the form of small round
drops of irregular softish semi-solid particles within the cytoplasm
of cells : afterwards the drops run together and are then excreted
into the cell-sap where they accumulate.
Oils and fats are reserve plant-foods, and are consequently
most abundant in the endosperm and cotyledons of seeds, and
in certain fruits. The seeds of the rape plant contain on an
average 42 per cent. ; flax-seeds (linseed), 36 per cent., and cotton
seeds, 25 per cent, of oil.
. The various kinds of ' Oil-cakes ' used for feeding cattle are
formed from the residue of different seeds and fruits, the greater
164 CHEMICAL COMPOSITION OF PLANTS
c
portion of whose oil has been extracted from them by crushing
and other means.
Ex. 91. Cut thin sections of the seeds of the almond, rape, Brazil-nut
and linseed. Mount in water and examine with a high power : note the
round bright oil-drops in the cells, and in the water round the section.
3. Volatile or essential oils. To these compounds are due
the aroma or odour of various plants, such as roses, mint, hops,
and lavender.
Many essential oils are composed of carbon and hydrogen
only, while others contain oxygen
in addition to these elements.
They frequently occur in the
form of drops in the cytoplasm
of the cells, and are sometimes
accumulated and deposited in
special parts of glandular hairs
and other receptacles.
4. Organic acids. The com-
monest examples of these com-
pounds found in the cells of
green plants are oxalic, malic,
,. , , , citric, and tartaric acids. They
FIG. Bo. a Single large crystals of
calcium oxalate in ceils of the parenchyma are met with either in the free
of a red clover leaf; b crystal-aggregates
from a rhubarb leaf; c raphides from a State, OF Combined With VariOUS
leaf of a fuchsia.
organic or mineral bases to
form acid and neutral salts.
The commonest acid in plants is oxalic acid, which occurs,
free, or more commonly combined with calcium or potassium,
in the parenchymatous tissue of leaves, stems and roots ; to the
acid potassium salt, is due the sour taste of the leaves of SorreJ
(Rumex acetosd) and Wood-sorrel (Oxalis acetoselld).
Crystals of calcium oxalate are very common in the tissues
of a great variety of plants; they are formed in vacuoles within-
the cytoplasm, and occur in the form of (i) single crystals (a,
PROTEINS OR ALBUMINOIDS
I6 S
Fig. 80)^(2) radiating crystal aggregates (), or (3) bundles of
needle-shaped crystals or raphides (c). The latter form is
frequent in the cells of many monocotyledons.
Malic, citric and tartaric acids are also found free or combined
with calcium or potassium, especially in unripe fruits of various
kinds. A lemon contains from 5 to 7 per cent, of free citric acid.
Ex. 92. Mount a very small portion of rhubarb jam in water, and look
for crystal-aggregates of calcium oxalate resembling b> Fig. 80. Many will
be observed within the thin parenchymatous cells present in the jam.
Ex. 93. Treat some clover, vetch, fuchsia and other leaves with Eau de
Javelle as in Ex. 75, wash in water and mount a small piece in glycerine :
note the form of the crystals of calcium oxalate, and their position in the
leaves. In which special tissues of the leaves are they most abundant ?
II. NITROGENOUS ORGANIC SUBSTANCES.
These compounds contain nitrogen and frequently other
b
FIG. 81. i Transverse section of a wheat-grain, p Pericarp ; a l aleuron-layer ' ; 6 starchy
part of the endosperm ; /"furrow at back of the grain.
a Part A of i (enlarged 160 diameters), t Pericarp ; a ' aleuron-layer ' showing small
aleuron-grains and a central nucleus within each cell ; b cells of endosperm containing starch-
grains.
elements such as sulphur and phosphorus, in addition to carbon,
hydrogen and oxygen.
The most important examples are the proteins or albuminoids
amides and alkaloids.
i. Proteins or albuminoids. The proteins are exceedingly
166 CHEMICAL COMPOSITION OF PLANTS
complex compounds to which no chemical formula can yet be
given. They are generally slimy like the white of an egg, and
like the latter substance many of them coagulate on heating;
some of them are soluble while others are insoluble in water.
The simplest proteins are composed of carbon, hydrogen, oxygen,
nitrogen and sulphur; they contain from 15 to 17 per cent of
nitrogen and from to 3 per cent, of sulphur.
As protoplasm consists largely of proteins, they are met with
in all living parts of plants : moreover some of these compounds
are found dissolved in the cell-sap.
Certain proteins are stored in the vacuoles and cell -sap of seeds
and other resting-organs as nitrogenous reserve -food in the form
of round or irregularly-shaped solid grains; such grains are
termed akuron- si protein-grains. In cereals the aleuron-grains
are very small and round, and are chiefly stored in the outermost
cell layers of the endosperm (Fig. 81). In other starchy seeds
such as beans and peas they are small, but in many oily seeds
such as those of the castor-oil plant and Brazil-nut, the aleuron-
grains are large, and generally contain a small round particle or
globoid of calcium and magnesium phosphates, together with a
larger or smaller protein-crystal or crystalloid.
The seeds of the lupin contain on an average about 34 per
cent., beans 24, wheat-grains 13, barley-grains 10, straw 3,
potatoes 2, and turnips about i per cent, of proteins.
Solid proteins stain a yellow colour with iodine.
Ex. 94. (a) Divide a wheat-grain in two transversely : then cut a thin
section to include a small portion of the pericarp and aleuron-layer as in Fig. 81.
Mount in dilute glycerine and run a drop of iodine solution under the cover-
slip : note the colour of the starch-grains and the aleuron-grains.
(b) Cut a similar section of a barley and an oat grain. Are the aleuron-
layers in these grains the same as in wheat ?
Ex. 95. Cut sections of the cotyledons of beans and peas: mount and
examine in dilute glycerine : note the small aleuron-grains in the cells along
with large starch-grains : stain with iodine and re-examine.
2. Amides. These are soluble crystalline nitrogenous com-
ALKALOIDS 167
pounds found dissolved in the cell-sap. Most of them are amido-
acids or simple derivatives of the latter. They are reserve-foods
chiefly present in the rhizomes, bulbs, tubers and roots of plants
and rarely in resting seeds.
The most widely distributed representative is asparaginc, which
is present in the parenchyma of almost all parts of plants : it is
more particularly abundant in the young shoots of asparagus,
sprouts and tubers of the potato and in seedlings of lupins, vetches
and other leguminous plants grown in the dark.
Other common amido-acids are glutamine, betaine, leucine, and
tyrosine met with in the mangel, sugar-beet, turnip and other
roots.
3. Alkaloids. The alkaloids are organic compounds of a
basic nature ; most of them are poisonous and form the active
principle of many plants used as drugs. The most familiar
examples are morphine^ obtained from the opium poppy, nicotine
from the tobacco plant, coninc from hemlock, and strychnine
from Strychnos Nux vomica.
CHAPTER XII.
THE COMPOSITION OF PLANTS (continued).
i. The elementary constituents of plants. Chemical analysis
has shown that the following elements are always present in the
compounds which form the body of a healthy green plant,
namely, carbon, hydrogen, oxygen, nitrogen, silicon, sulphur,
phosphorus, chlorine, potassium, sodium, calcium, magnesium
and iron.
In sea-weeds bromine and iodine are usually present, and
many other elements, such as aluminium, zinc and copper, have
been occasionally discovered in small quantities in certain
species of plants.
On burning the dry matter of a plant, the carbon, hydrogen,
oxygen and nitrogen within it escape into the air in the form
of water, carbon dioxide, free nitrogen and other volatile
compounds : the other elements are left in the ash.
While chemical analysis enables us to determine the particular
elements of which the body of a plant is composed, it does
not furnish a means of deciding which and how many of these
elements are necessary for the plant's existence.
Since the majority of plants contain no zinc, tin or lead, it is
clear that these elements and others which are only occasionally
present are not necessary for plant-growth. On the other hand,
that carbon, hydrogen, oxygen and nitrogen are absolutely
essential may be inferred from the fact that these elements are
essential components of the organic compounds of which the
cell walls and protoplasm are constructed. It does not, however,
183
ELEMENTARY CONSTITUENTS OF PLANTS 169
follow that elements which are invariably present are therefore
absolutely necessary for the life of a plant.
To determine with certainty which elements are indispensable
for proper nutrition and growth, cultivation experiments must be
carried out in soil or other media, the composition of which is
accurately known, and which can be regulated and kept under
control. This is best achieved by the methods of water-culture
and sand-culture^ which consist in growing the plants in pure
water or in pure sand, to which are added compounds of the
various elements whose influence is to be studied. By means of
such experiments it has been proved that only ten elements are
really essential for the growth of green plants, namely, carbon,
hydrogen, oxygen, nitrogen, sulphur, phosphorus, potassium,
magnesium, calcium and iron ; possibly to this list chlorine
should be added.
All attempts to grow plants in soil, water or air from which any
one or more of these elements are excluded end in failure. The
other elements sometimes found in plant ash are superfluous;
even sodium and silicon, which are present in all plants growing
in ordinary soils, are not indispensable, for healthy specimens
capable of producing seed can be reared without them.
Ex. 96. Water-culture. For the growth of plants in nutrient solutions
glass cylinders or wide-necked bottles holding about 600 or 700 c.c. of water
should be used.
Before use the cylinder must be rinsed out first with nitric acid and then
thoroughly washed with distilled water. It should be fitted with a cork bung
through which two holes should be bored, one for the exit of the stem of the
plant to be grown, the other into which a short glass tube is fitted being con-
venient for adding water to replace that which is lost by transpiration.
The solutions to be used must not contain more than from 2 to 5 grams of
dissolved salts in 1000 grams of water : a higher concentration is detrimental
to growth.
Moreover a slightly acid reaction should be maintained, alkaline solutions
being injurious.
For complete nutrition the composition of the solution may vary consider-
Ably so long as the essential elements are present in a suitable state for
Absorption by the roots of the plants. The following solution contains all
170 CHEMICAL COMPOSITION OF PLANTS
that is needed by green plants, the necessary carbon being obtained from the
carbon dioxide of the air :
Water, .
Calcium nitrate, .
Potassium chloride,
Magnesium sulphate,
Grams
1500
2
i
4
Grams.
Acid potassium phosphate
(KH 2 P0 4 ),
A few drops of ferric chloride
solution.
For demonstration purposes buckwheat, barley, maize, small dwarf-beans,
and wallflowers are easily grown. Seeds should be germinated in damp
sawdust or on damp blotting-paper, and when
the seedlings are large enough to handle they
should be arranged as in Fig. 82, so that their
roots dip into the culture solution, their stems
being allowed to develop through the hole in
the cork (c). Seedlings of maize, barley and
beans may be fastened in position by means of a
pin pushed through the side of the pericarp or
the seed-coat into the lower side of the cork ; or
they may be supported by inserting cotton wool
in the hole through which the stem emerges.
It is important to see that only the roots dip
into the solution : wetting the endosperm,
cotyledons, or hypocotyl frequently leads to ill-
health and death of the plant.
The sides of the glass cylinder should be
covered with cardboard or several thicknesses of
paper to prevent access of light and heat to the
solution : or the cylinder may be sunk in a box
containing cocoa-nut fibre.
Avoid placing the culture in the direct sun-
light so that the solution in which the roots are glas> vessel ; s culture solution :
r ._J 1. 1 _
immersed may remain cool.
c perforated cork bung.
In experiments extending over a period of several weeks the culture
solution should be changed every week, and the plant should be placed
occasionally for a day or two with its roots in distilled water, or water con-
taining a small amount of calcium sulphate.
Ex. 97. Fit up a water-culture as above but do not add ferric chloride or
any other compound of iron to the solution : compare the growth of the plant
with one growing in a complete solution.
Ex. 98. Note the differences between plants growing in a complete solu-
tion as above and some growing in the following solutions in which nitrogen
and potassium are respectively missing.
ELEMENTARY CONSTITUENTS OF PLANTS 171
SOLUTION WITHOUT NITROGEN.
Grams.
Water, .... rooo
Calcium sulphate, . . I
Acid potassium phosphate, .
Magnesium sulphate, . .
Potassium chloride. . . A
SOLUTION WITHOUT POTASSIUM.
Grams.
Water, . .
Calcium nitrate, *
Magnesium sulphate,
Acid sodium phosphate
Sodium chloride, .
1000
I
To both the solutions add a few drops of ferric chloride solution.
2. Essential elementary constituents of plants. The follow-
ing is a brief account of the elements which are absolutely
necessary for the nutrition of plants.
(i) Carbon. Carbon is one of the essential constituents of
protoplasm, and enters very largely into the composition of the
cell-wall, and many reserve foods of plants. The amount present
in plants usually amounts to between 40 and 50 per cent, of the
dry matter within them. The greater portion of it is derived
from the carbon dioxide of the atmosphere, but in some cases,
and perhaps in all, a certain amount of carbon is taken from the
soil in the form of organic compounds.
Fungi among the lower, and Dodder (Cuscutci), (p. 605),
Broom-rape (Orobanche\ (p. 607), and Bird's-nest orchis (Neottia)
among the higher plants, obtain their carbon in the form of
organic carbon compounds from living animals and plants, or
from the decaying remains of these organisms.
(ii) Hydrogen and oxygen are found combined with carbon
and other elements in the protoplasm, cell-wall, sugars, fats, and
other compounds present within the plant.
Hydrogen is a constituent of water, and in this form is chiefly
absorbed from the soil. Between 5 and 6 per cent, of the dry
matter of a plant is hydrogen.
The amount of oxygen present in the dry matter of plants
averages between 35 and 45 per cent. It is absorbed in a free
state from the air in the respiration-process, and is also taken up
from the soil in nitrates, sulphates, carbonates and phosphates.
(iii) Nitrogen. This element enters into the composition of
172 CHEMICAL COMPOSITION OF PLANTS
protein or albuminoid substances, amides and a few other less
important organic substances ; it is also found in the inorganic
nitrates which are frequently present in small quantity in the
cell-sap of plants.
The amount of nitrogen present is especially high in the seeds
of leguminous plants, being in peas 4*8 per cent., in beans 5
per cent., and in yellow lupins as much as 7 per cent, of the
dry matter : in starchy cereal grains such as wheat, barley, and
maize the amount is usually less than 2 per cent.
The vegetative parts of leguminous plants are generally richer
in nitrogen than those of most other plants : for example, in red
clover and lucerne cut in bloom the amount present is from 2
to 2\ per cent., while in grasses the average amount is about if
per cent, of the dry matter.
With the exception of leguminous plants which derive most of
their nitrogen from the free nitrogen of the atmosphere (see
p. 806), green plants take up this element from the soil chiefly in
the form of nitrates. It has been proved by means of water
cultures that they are also able to absorb and utilise the nitrogen
of ammonium compounds, but as the latter when applied to the
soil become changed into nitrates in the process of nitrification
(see p. 799) it may be said that nitrates are the chief natural
source of nitrogen for green plants.
Although it has been shown that most plants can grow equally
well with nitrogen in the form of ammonium salts as with nitrates,
Maz^ found that solutions of the former when more concentrated
than about '5 gram in 1000 damage the plants, whereas bad effects
are not visible with nitrates until the solution applied to the roots
contained 2 parts in 1000 of water.
Nitrogen when supplied to plants in considerable quantity
specially increases the luxuriance of their leaves, stems and
vegetative organs ; such plants are dark green in colour, and
show little tendency to produce reproductive organs and seeds.
(iv) Phosphorus. Phosphorus is a constituent of several kinds
POTASSIUM 173
of protein compounds, and is more especially abundant in the
protein of the nucleus of plant-cells.
Besides being met with as a constituent element of organic
compounds, it is often present in the form of inorganic phosphates.
Phosphorus constitutes a large proportion of the ash of seeds,
and without an adequate supply of this element, the formation
and development of seeds do not take place satisfactorily.
The amount of phosphorus calculated as phosphoric acid in the
ash of wheat-grains averages from 45 to 50 per cent, and in
beans about 40 per cent. : in the ash of the vegetative parts the
amount is considerably smaller, e.g., in wheat-straw about 5, in
turnips 7, in hay 6, and in potato tubers about 17 per cent.
Phosphorus is absorbed by plants from the soil in the form
of phosphates of potassium and calcium.
(v) Sulphur enters into the composition of proteins, although
the amount is small, rarely exceeding 2 per cent. It is also
a constituent of ' mustard-oil ' obtained from many cruciferous
plants, and is found in the form of inorganic sulphates in which
condition it is absorbed from the soil.
(vi) Potassium. This element is specially abundant in the ash
of the young actively-growing part of plants where cell-division
is going on, and probably is an essential constituent of the
protoplasm of all cells. It also exists combined with tartaric,
oxalic, malic, and other organic and inorganic acids in the cell-sap.
Tissues containing large reserves of carbohydrates are frequently
rich in this element ; for example, in potato tubers 2*3 per cent,
in grapes about 3 per cent., and in 'mangels 4 per cent, of the dry
matter is potash (K 2 O).
It is taken up from the soil chiefly as nitrate, chloride, car-
bonate, sulphate and phosphate.
The part which potassium plays in the economy of the plant
is not known with certainty. According to De Vries its salts
are especially concerned with the maintenance of the turgidity
of the cells, and as the latter condition is essential for growth
174 CHEMICAL COMPOSITION OF PLANTS
the particular abundance of the element in growing tissues is
thus partially explained.
It has been observed that the ' fixation of carbon ' in green
tissues ceases when potassium isabsent, and cereals and peas grown
with an insufficient supply produce small thin grains and seeds.
The place of potassium in the economy of the plant cannot be
taken by any of the other nearly allied elements such as sodium
and lithium.
(vii) Calcium. Fungi appear to be able to dispense with calcium,
but for green plants it is an essential element. It is absorbed
from the soil in the form of a nitrate, phosphate or sulphate.
In the young parts of plants calcium is generally present in small
quantity only and in some instances it may be missing altogether
from such parts for a time, its absence leading to no apparent in-
jurious effect. It is most abundant in the older parts of plants, such
as fully-developed and dying leaves, bark and pith, and occurs in
the form of salts of organic and inorganic acids more especially as
oxalate and carbonate. The amount of lime (CaO) in the ash of
barley, oat, and wheat straw is generally about ^ per cent.
Although seedling plants may continue to grow for one 01
two months without calcium, they always appear stunted under
such conditions and present other features of ill-health ; if calcium
compounds are still withheld death takes place.
Like some other essential elements calcium plays a many-
sided role in plant-nutrition.
Oxalic acid and soluble oxalates are formed in certain plants
and when present in very slight excess act injuriously upon the
nucleus and other cell-constituents ; in the presence of calcium
salts their accumulation and poisonous action is prevented by the
formation of insoluble calcium oxalate.
Calcium is, however, not exclusively utilised for the neutralisa-
tion of oxalic acid, for there are many plants which never contain
oxalic acid, and yet it is found that such plants still require this
element for perfect growth. The assumption that calcium oxalate
NON-ESSENTIAL CONSTITUENTS 175
is a waste product is not apparently true in every instance, for
there is evidence to believe that it is dissolved again sometimes
and utilised as a reserve of calcium.
(viii) Magnesium is found in the ash of all parts of the plant,
but more especially in that of seeds. About 1 2 per cent, of the
ash of wheat grains consists of magnesia (MgO), while the ash of
the straw and vegetative parts contains less than 2 per cent.
Magnesium is taken from the soil, chiefly as carbonate and
sulphate, but its use to the plant is still very obscure.
(ix) Iron. The amount of iron in green plants is generally
very small, rarely exceeding 0*2 per cent, of the ash. It is,
nevertheless, absolutely necessary for their nutrition since with-
out it no chlorophyll is formed. Sufficient iron is present in
seeds for the production of a certain amount of chlorophyll,
and the first few leaves of seedlings grown in culture solutions
free from iron are green \ the subsequent ones are, however,
pale and incapable of utilising the carbon.
3. Non-essential elementary constituents of plants. Some
of the elements are of such rare and abnormal occurrence in
plants that they need not be mentioned. Others, such as silicon,
sodium and chlorine, although found to be non essential to the
growth of green plants, are universally met with in the ash and
demand brief notice.
Although healthy plants can be grown in the absence of several
elements, which are commonly met with in ordinary plant ash,
these so-called non-essential constituents may be, and probably
are, of use in stimulating or depressing the activity of various
functions carried on by plants.
Silicon is specially abundant in the cell- walls of the external
portions of the stems and leaves of barley, wheat, oats and grasses
generally : more than one-half of the total ash of the cereals
consists of silica (SiO 2 ).
The accumulation of silicon in the cell-walls was formerly
supposed to be the cause of the rigidity and firmness of well-
grown straw and the * lodging ' of cereal crops was attributed to a
176 CHEMICAL COMPOSITION OF PLANTS
lack of this compound. * Lodging ' is, however, due to a weakness
caused chiefly by want of proper amount of light for normal
growth, and firm-strawed, well-developed plants of maize, oats,
and other cereals have been grown in water-cultures without
silicon. Moreover, analysis has shown that the straw of ' lodged '
crops generally contains more silicon and is much more brittle
than straws of crops which have stood upright.
Jodin grew four generations of maize plants without any silicon.
Cultures of oats from which this element is missing do not
yield so much grain as those to which it is applied.
Silicon is absorbed from the soil in the form of soluble silicates,
the bases with which the latter are associated being apparently
utilised in the nutritive processes.
Sodium in the form of sodium chloride is frequent in all
plants, but is absorbed in greatest amount by halophytic plants
which flourish on salt-marshes near the seashore, or inland near
salt-mines and salt-lakes, where the amount of salt present in
the soil is more than can be tolerated by ordinary inland plants.
Many halophytes, such as Glasswort (Salicornia herbacea L.),
Saltwort (Salsola Xa/iL.), beet and mangel, and species of A triplex,
belong to the Chenopodiacese (p. 356). Several cultivated cruci-
ferous plants, such as the cabbages and seakale, are descendants
of halophytes ; asparagus is another example of the same class.
Culture experiments have shown that even the most typical of
these halophytes can be grown without salt ; nevertheless when sup-
plied with it, they present a different appearance and have different
physiological characters from plants deprived of the compound.
Under the influence of an abundance of salt the vegetative
organs become plumper, more fleshy and succulent and transpire
less than they do when grown without much salt.
Plants, such as the cereals and others not habitually growing
near the sea, are killed by solutions containing more than i or i \
per cent, whereas sea-beet and certain species of Atriplex are
not destroyed by solutions containing 3 or 4 per cent, of salt.
CHAPTER Xin
OSMOSIS : ABSORPTION OP WATER.
i. Osmosis. When a bladder filled with a solution of sugar has
the opening into it tightly tied with string and then placed in a
vessel full of pure water it is found that a considerable amount
of the latter soon passes through the walls of the bladder into
the interior and mixes with the sugar-solution, in spite of the
fact that no visible openings are present through which the
water travels.
The result of this inward transference of water is that an out-
ward pressure is set up within the bladder and it becomes more
and more distended, just as it would be if water or air were
forced into it mechanically. The amount of internal pressure
set up under these circumstances depends upon the amount
of sugar dissolved in the sugar-solution and also upon the
temperature at which the experiment is made : with a con-
centrated solution a greater pressure is produced than when a
weak solution is used, and at a high temperature the pressure is
greater than at a lower one.
Similar internal pressure tending to expand the bladder is
observable when solutions of potassium nitrate, copper sulphate,
and many other substances are used instead of sugar solution.
Each of these soluble compounds possesses a different power of
attracting water through the walls of the bladder ; the pressure
set up by a solution of say one per cent, of sugar is not the
same as that induced by a solution of one per cent, of potassium
nitrate.
In these experiments it will be found that while pure water
177
OSMOSIS: ABSORPTION OF WATER
passes inwards through the walls of the bladder a certain amount
of the sugar or the other soluble compounds employed passes
outwards into the pure water within the vessel : and it is noticed
that the process of diffusion or passage of the dissolved substances
goes on through the membrane until the percentage, composition,
or strength of the solution is the same inside and out.
Certain membranes are, however, known which allow water to
pass through them but which are not permeable to sugar and
other dissolved compounds.
The diffusion or passage of liquids and solutions of sub-
stances through membranes in which no visible openings are
present is termed osmosis: the pressure set up in the interior
of closed permeable membranes is spoken of as osmotic pressure,
and the dissolved substances upon which the pressure is primarily
dependent may be designated osmotic substances.
A bladder or other structure distended by osmotic pressure
becomes firm or rigid instead of limp and flabby and in this
condition is spoken of as turgid,
Dissolved in the cell-sap of all living plant cells are osmotic
substances, such as sugars and salts of various kinds, which have
the power of attracting water into the interior, and when plant
cells are immersed in pure water they become turgid.
In all living parts of plants which are adequately supplied
with water, and especially in those regions in which active growth
is going on, the cells are distended by osmotic pressure, and this
state of turgidity is the cause of the elasticity and firmness ex-
hibited by the thin-walled living parenchymatous tissues of leaves,
growing-points, and other delicately-constructed portions of plants.
The pressure within young turgid cells usually amounts to five
or ten atmospheres and under its influence the cytoplasm is forced
outwards into close contact with the cell-wall at all points ; the
cell-wall becomes stretched until its elastic recoil equals that of
the outward pressure. In the cells of fruits containing consider-
able amounts of osmotic substances in the cell-sap the pressure set
OSMOSIS 179
up in wet weather when abundance of water is conducted to them
is sometimes sufficient to burst the cell-walls and the fruits split.
The osmotic properties of a plant cell are, however, not the
same as those of a bladder filled with sugar-solution, for in many
instances cells containing sugar or other substances do not allow
these to pass out into water in which the cells may be immersed.
It is obvious that even a very slight permeability of the sub-
stances to which turgidity is due would make it practically
impossible for any submerged water-plant to remain turgid, and
the accumulation and retention of sugars and other soluble
substances in the roots of beet and similar plants growing in
damp soil would be equally difficult if the protoplasm and walls
of the external cells were permeable to such compounds.
Whatever substances pass into or out of a living plant cell
must permeate both the cell-wall and the thin lining of cytoplasm.
While pure water finds a ready passage through both membranes
the cytoplasm is very frequently either quite impermeable or per-
meable in a very different degree to many substances which easily
travel through the cell-wall. Moreover, the permeability of the
cytoplasm to any particular substance is not the same at all times.
When a turgid cell is immersed in a solution of a substance
whose attraction for water is greater than that possessed by the
substances dissolved in the cell-sap, a larger or smaller amount
of water is abstracted from the cell and the osmotic pressure is
reduced, the cell becoming smaller and more or less limp. If
the vitality of the cytoplasm is not destroyed and the osmotic
action of the solution continues, more water is abstracted from
the vacuole, but the cytoplasm instead of remaining in contact
with the cell-wall and allowing the solution to penetrate into the
vacuole, shrinks away from the cell-wall and takes the form of a
nearly spherical hollow ball in the centre of the cell-cavity : a
living cell in this condition is said to be plasmotystd. The space
between the cell-wall and the shrunken cytoplasm becomes occu-
pied by the solution which has penetrated inwards through the
180 OSMOSIS I ABSORPTION OF WATER
cell-wall, but none is allowed to pass through the living cytoplasm.
Moreover, the osmotic substances dissolved in the cell-sap do
not travel outwards through the cytoplasm. Cells plasmolysed
in this manner regain their turgid condition when placed in pure
water ; the plasmolysing substance which has passed through the
cell-wall diffuses out and water again enters the vacuole so that
the cytoplasm becomes forced into contact with the cell-wall.
When a leaf or a branch with leaves upon it is cut from a
plant and left exposed to the air, water soon escapes from the
cells in the form of vapour ; the turgidity of the cells is rapidly
reduced and, in consequence, the leaves instead of maintaining
their elasticity and firmness, become limp and unable to support
themselves in a normal position.
This flaccid state of * wilted ' or * faded ' parts of plants is always
brought about by the loss of water from the cells whereby their
turgid stretched condition is reduced, although the conditions
which lead to the loss of water is not the same in all cases.
If the loss of water from a cut shoot has not gone too far, and
the cytoplasm is still living, it is generally possible to renew the
former turgid state of its cells by placing the end of the stem in
water, or by forcing water into the * wilted' shoot as in Ex. 105.
From various extensive observations and experiments it is
evident that the passage of substances in solution into or out
of a cell, is under the control of the living cytoplasm ; the
phenomena of turgidity and other osmotic properties are de-
stroyed when death of the cytoplasm takes place.
Ex. 99. Stretch a piece of wetted bladder across one end of a glass lamp-
chimney and firmly tie it with string ; then fill about of the chimney with
a saturated solution of sugar, and suspend it in a vessel of water, so that
the sugar-solution inside the glass chimney is level with the surface of the
water outside. Allow it to remain for a few hours ; note that the water
passes inwards through the bladder into the sugar solution and causes the
level of the latter to rise.
Ex. 100. Repeat the preceding experiment, using a strong solution of
copper sulphate or potassium bichromate. Observe if the copper sulphate
or potassium bichromate passes outwards and colours the clear water.
OSMOSIS
iSl
Ex. 101. Cut a few slices, about J of an inch thick, through a beetroot
or sugar beet ; wash them in distilled water and place
(1) Some in a vessel in distilled water.
(2) Others first in boiling water for a minute or two to kill the cytoplasm
of the cells, and then into a vessel containing distilled water. Allow them
to remain for four hours ; afterwards take out a small quantity of water
from each vessel and test for sugar by boiling with a drop or two of
hydrochloric acid and subsequently adding Fehling's solution (see Ex. 80).
Ex. 102. Cut a transverse section through a portion of a garden beetroot.
First wash it in water in a watch-glass, and then mount in water and
examine with a low power of the microscope.
( i) Observe the presence of pink cell-sap in the uninjured cells ; note that
it does not escape into the surrounding water.
(ii) Run under the cover-glass a few drops of a 4 per cent, solution of
common salt, and observe that as the colourless solution of salt penetrates
into the cell plasmolysis begins and the cytoplasm recedes from the cell-
wall. Notice that although water is withdrawn through the cytoplasm, the
latter does not allow the colouring matter of the cell-sap to
diffuse outwards, for the salt-solution which passes inwards
through the cell-wall remains uncoloured.
(iii) Remove the cover-glass when the cells have become
plasmolysed, wash away the salt-solution by soaking the
section for a second or two in pure water, and then re-
mount in water.
Examine with microscope and note that the cytoplasm
gradually recovers its original position close to the cell-
wall.
Ex. 103. Cut a similar section of a piece of beetroot,
and dip it for a moment into methylated spirit to kill
the cytoplasm of the cells ; wash quickly and then mount
in water ; note that the pink cell-sap now diffuses out into
the surrounding water.
Ex. 104. Make careful measurements of portions 2 or
3 inches long of the young primary roots of beans and
peas, young hop shoots, young flower-stalks of a dandelion, and other turgid
portions of plants. Place them in a 10 per cent, solution of salt for six or
seven hours and measure again ; note the shrinkage and flabbiness of the
parts due to loss of turgidity of the cells.
Ex. 105. Cut off a shoot of a Jerusalem artichoke and leave it to wither
in an ordinary room for about an hour ; note the limp state of its leaves
after that time. After cutting off half an inch of the stem fasten it to a
bent glass tube by means of a short piece of rubber tube (r) as in Fig. 83.
FIG. 83
182 OSMOSIS: ABSORPTION OF WATER
Firmly tie the rubber tube to the glass tube and to the stem of the plant,
and then partially fill the glass tube with water taking care that no air is left
between the end of the stem and the water. Pour in mercury until the level
in the free limb of the tube is considerably higher than in the other (6) ; the
pressure of the mercury will force the water (a) into the shoot and the leaves
will soon begin to assume their natural position and firmness.
2. Absorption of water. In all actively-growing plants water
forms considerably more than half their total weight ; it satur-
ates the living protoplasm and the cell-walls, and is the chief
component of the cell-sap.
Water is utilised by plants for maintaining the turgidity
of their cells, and a small amount is employed as a food-material.
It is also of the greatest importance for the purpose of dissolving
the various foods present in the plant and conveying them to the
different organs requiring nourishment. Moreover, the absorp-
tion of water is the only means which a plant possesses of
obtaining the various essential food-materials which are derived
from the soil, for it is only when these necessary constituents
are dissolved that they can find an entrance into plants : no
solid particles of manures or other components of the soil, how-
ever small, are taken up by them.
Water and the dissolved compounds which plants absorb pass
into them by osmosis and therefore only gain an entrance
through organs whose external cell-walls are uncutinized or
unsuberized. During the life of an ordinary farm or garden
plant, the absorption of water and the absorption of dissolved
food-materials are necessarily carried on at the same time : they
may, however, be treated as separate phenomena.
The nature of the dissolved substances which are absorbed
by plants, and the conditions which govern their absorption, are
dealt with in chapters xii. and xv. ; at present it is advisable to
consider the absorption of water alone.
Plants which live completely immersed in the sea and in
ponds and rivers rarely have a well-developed cuticle and take
ABSORPTION OF WATER 183
in water through the surfaces of their stems and leaves as well
as through their roots, but the crops of the farm and garden
and all ordinary land-plants absorb all the water which they
require from the soil by means of their roots only.
When the soil in a pot in which a plant is growing is allowed
to become dry the plant begins to droop and wilt, and no amount
of syringing or even immersion of the leaves and stems in water
will completely revive and sustain the life of the plant so long
as the soil is kept dry.
In good well-drained soil, the chief amount of rain which falls
upon it sinks through into the subsoil, but a certain amount
remains behind in the form of more or less thin films of water
surrounding each solid particle of which the soil is composed.
In such soil some water is retained in the minute spaces
present in it, and a certain amount of water travels upward from
the subsoil by capillarity into these spaces in the upper layers
of the soil. Good well-drained soils, while thus retaining an
adequate supply of water, allow a free penetration and circula-
tion of air within them. Only in water-logged soils totally
unsuited to the growth of ordinary farm and garden crops are
all the spaces between the component particles of the soil
completely filled with water, and air excluded.
Soon after the appearance of the primary root from a seed
secondary roots spring from it, and from these new roots arise,
so that the soil becomes penetrated in all directions by fine
rootlets, near the ends of which numbers of root-hairs are
developed. The growing rootlets push their way through the
small crevices in the soil and the root-hairs are brought into
close contact with the small particles of soil and with the films
of water surrounding the latter.
Formerly the absorption of water was supposed to take place
through the root-caps which were termed * spongioles ' ; experi-
ments, however, have shown that plants are able to absorb all
the water they need when the root-caps are exposed to the air
184 OSMOSIS: ABSORPTION OF WATER
or destroyed, so long as the other young parts of the roots are
kept in contact with water.
It has been experimentally proved that it is only through the
root-hairs and the youngest parts in the immediate neighbour-
hood of the root-hairs that the absorption of water occurs :
through the older parts on which the root-hairs have shrivelled
and which have become covered with a tissue of cork-cells water
is unable to penetrate.
The walls of the root-hairs consist of ordinary uncutinized
cellulose through which water readily passes, and it is on
account of the existence of osmotic substances in the cell-sap
within the hairs that water with which they come in contact is
attracted into them.
After carrying on their work for a short time they wither and
die, but before this occurs a new set of hairs arises on the
extending rootlet.
The greatest development of root-hairs occurs upon roots
which are allowed to grow in damp air or in a moderately dry
soil. When roots are immersed altogether in water, root-hairs
are generally absent; the necessary absorption in such roots
is carried on by the unextended superficial cells of the piliferous
layer, there being no need for the extension of these cells into
long hairs.
In very dry soils the development of root-hairs is feeble or
entirely checked.
On account of the delicate nature of the root-hairs it is not
possible to remove a plant from the soil without breaking the
connection of the hairs with the fine particles of earth and
permanently destroying many of them ; transplanted plants,
therefore, always suffer for want of water until new hairs are
formed on the rootlets. Among certain plants new roots and
root-hairs do not form readily and such plants cannot be trans-
planted. When trees or other plants are removed, it is advisable
to specially preserve the youngest rootlets from which fresh
ABSORPTION OF WATER 185
growths are most easily produced, and after re-planting her-
baceous plants exposure to a dry atmosphere, or to strong light
and other influences which promote loss of water from the leaves
by transpiration (see chap, xiv.), should be avoided for a time
wherever possible.
The osmotic absorption of water by the root-hairs of plants only
goes on when the following conditions are fulfilled, namely :
(i) A certain degree of warmth of the surrounding soil,
(ii) Access to fresh air ; and (iii) A suitable supply of water.
Cabbages and many other plants are able to absorb consider-
able amounts of water at freezing-point, but at the low tempera-
tures of winter absorption generally ceases or is vastly decreased
and it is not until the return of warm days in spring that the
activity of the roots is manifest.
The application of water from wells to the roots of tropical
and sub-tropical plants growing in pots in warm houses frequently
checks their absorptive power by lowering their temperature
considerably.
Sachs showed that the absorption by a tobacco plant at a
temperature of 4 or 5 C. was so small that withering com-
menced in spite of the fact that the roots of the plant had
access to an abundance of water.
In consequence of the presence of a considerable amount of
water which requires much heat to warm it, the temperature of
imperfectly-drained soils is usually lower than that at which the
roots of ordinary farm and garden plants do their work best.
Moreover, such soils do not allow of the free circulation of fresh
air within them, and the respiration process carried on by the
living protoplasm of the root-hairs is interfered with.
Without the access of an adequate supply of oxygen, or where
there is much carbon dioxide in the soil, poisonous compounds
are formed within the roots as the result of imperfect respiration
and the plants become unhealthy. Over-watered plants growing
in pots commonly exhibit injuries of this character.
1 86 OSMOSIS I ABSORPTION OF WATER
Roots die or develop badly when plants are transplanted and
put into the soil too deeply. Although the root-hairs come
into very intimate contact with the small particles of earth, and
are specially adapted to use the thin films of water surrounding
the latter, they are not able to withdraw the whole of the water
which a soil is capable of holding. When soils are allowed to
dry, plants growing in them begin to wither as soon as the water
present sinks below a certain amount, which varies with the
composition of the soil in question. Beans, tobacco and
cucumber plants have been found to wither and die in good
garden soils containing 12 to 15 per cent, of water and in loams
containing 8 per cent.
Ex. 106. Grow a dwarf-bean in a pot of sandy soil and one in a pot of good
garden soil. When the plants have three or four well -developed leaves allow
the soil to become dry and when the plants are dead shake out the soil from
each pot and determine what percentage of water remains in it. To do this,
weigh a porcelain dish ; then place a small amount of the soil in the dish and
weigh again ; the difference gives the weight of the soil taken. Place the
dish with the soil in a * water-oven ' to drive off all the water ; leave for five
or six hours and when cool weigh again ; the loss gives the amount of water
which has evaporated from the amount of the soil taken ; from these weights
calculate the percentage loss of water.
Ex. 107. Select three seedling cabbages as near the same size as possible ;
take one of them up carefully with a small amount of earth with it so as to
damage the roots as little as possible ; the second take up and shake off all
the soil ; take up the third and after shaking off all the earth from its roots
pull off all the finest rootlets. Then transplant all three and notice the
further growth of the three plants for ten days.
3. Exudation-pressure. Boot-pressure: 'bleeding' of plants.
After water has been absorbed from the soil by the root-hairs, it
passes by osmosis from the latter into the adjoining parenchyma-
tous cells of the cortex (c, 2, Fig. 72). The cortical cells then absorb
from each other until they all become highly turgid, and the same
turgid condition is soon reached by the parenchymatous cells
within the vascular cylinder of the root. When a certain degree
of pressure is attained within the innermost parenchymatous cells
EXUDATION-PRESSURE I ROOT-PRESSURE 187
bordering on the wood-strands (w, 2, Fig. 72), the protoplasm
ot the former becomes permeable, and a portion of the cell-sap
within them is forced into the cavities of the vessels and tracheids
with which the cells are in contact.
The pressure thus set up by the turgid parenchymatous cells
of the cortex and the cells of the ground tissue within the
vascular cylinder of a root is termed root-pressure.
Under this pressure the vessels and tracheids of the vascular
bundles become filled with water, and on cutting off the stem of
a tree in spring after the roots have begun their absorptive work
and before the buds have opened, the water is forced out of the
cut end of the stump still connected with the root in larger or
smaller quantities ; such outflowing of water from plants which
have been cut is spoken of as c bleeding. 1 The liquid forced out
of a * bleeding ' plant is not pure water, but a solution containing
small quantities of various substances,- such as soluble carbo-
hydrates, acids, organic and inorganic salts, and proteids. In
the sugar maple the liquid contains over 3 per cent, of sugar
which in some parts of the world is profitably extracted from it
In the case of the vine, sycamore, birch and other trees,
'bleeding 1 may continue for several days, during which time
several pints of ' sap ' may be exuded,
By attaching a suitable manometer or pressure-gauge to the
stump of a ' bleeding ' stem, the pressure with which the sap is
forced out can be measured : in the vine it frequently amounts
to more than one atmosphere, or sufficient to support a column
of mercury 760 mm. in height.
The root-pressure of a stinging nettle was found to be sufficient
to balance a column of mercury 460 mm. in height, while that
of an ash tree was only able to support a column of 20 mm. of
mercury.
The phenomena of root pressure and 'bleeding* are best
observed in woody perennials, such as the vine, birch and
sycamore, in spring and early summer about the time when the
i88 OSMOSIS: ABSORPTION OF WATER
buds are opening. At this season, the warmth of the soil
encourages very active absorption by the roots and trie water
taken into the plant finds no outlet : the vessels and tracheids
of the young wood throughout the plant become, therefore,
gorged with water and cutting into the stems allows the water
to escape. Later in summer, however, when the leaves are
expanded, the water absorbed by the root and forced into the
vascular cylinder, travels through the stem and into the leaves, from
whence it escapes into the air in the form of vapour as described
in the next chapter. The rapid loss of water from the leaves
results in the removal of large quantities of water from the
cavities of the vessels and tracheids and these latter elements
of the wood are then found to contain considerable amounts
of air as well as water : plants cut at this season do not ' bleed.'
Moreover, the evaporation of water from the leaves goes on so
rapidly that a partial vacuum is created and a negative pressure
is set up in the vascular system of the plant; under such
conditions, instead of water being pressed out with considerable
force from the cut stump of a plant connected with its root,
the stump is found to absorb any water given to it, and not
until it has become saturated can a positive root-pressure be
detected.
Root-pressure and * bleeding* are not confined to trees and
shrubs, but are observable in greater or lesser degree in many
plants when evaporation of water from the leaves is retarded
or prevented. They may be as readily observed in many
herbaceous plants, such as the sunflower, potato, tobacco, dahlia
and maize, as in woody plants.
The force of root-pressure is usually highest in the afternoon
and lowest in the early morning. Like other vital processes, it
is influenced by external conditions : an increasing temperature
of the soil increases it.
Although the pressure set up by the osmotic activity of the
parenchymatous cells of the cortex and other parts of the root
EXUDATION-PRESSURE : ROOT-PRESSURE 189
and stem is not sufficient to force water to the top of tali trees,
it brings about the introduction of water into the conducting
channels and helps in the rapid translocation of water throughout
the vascular tissues of the plant.
When the absorptive activity of the root of a plant is encouraged
by warmth of the soil and at the same time the loss of water in
the form of vapour from the leaves is diminished or prevented
by a damp atmosphere, the plant becomes overcharged and
water is forced out of the tips and edges of the leaves in drops
which are frequently mistaken for dew-drops.
This emission of drops of water may be often observed on the
tips and edges of the leaves of such plants as balsams, ' Arum
lilies' and fuchsias when growing in warm houses in which a
damp atmosphere is maintained. Similar drops are sometimes
nseen in the early morning on the tips and edges of
the leaves of species of Troptzolum, Alchemilla,
and many wild plants after a warm night when the
sky has been overcast.
The * bleeding ' of cut stems and the exudation
of drops of water from uncut plants is not caused
exclusively by the osmotic pressure of the cells
in the root, but is due in some degree to the
parenchymatous cells of the leaves and the
medullary rays and wood parenchyma of the stem,
for ' bleeding * from the cut end of a leafy stem
which has no connection with a root can often
be induced by immersing its young and easily-
wetted leaves and stem completely in water.
The osmotic pressure which results in the
'bleeding* of plants when cut, or the forcible
emission of drops of water from leaves and other
parts is a general phenomenon observable in
FIG. 84. greater or lesser degree throughout the body of
the plant; it is best termed Exudation-pressure' or *bkeding-
b
a.
i9o OSMOSIS: ABSORPTION OF WATER
pressure? root-pressure being merely a special example of its
activity.
Ex. 108. Water a well-developed sunflower, tomato, or tobacco plant
growing in a pot as in Fig. 84, and place it in a warm shaded situation for
two or three hours. Then cut off the stem and fasten a glass tube to the
stump by means of a piece of rubber-tube (r). Pour in a little water and
tap the tube to displace air-bubbles ; mark the height at which the water
stands as at a. After a time a considerable amount of sap will be forced from
the cut end of the stem and will rise in the glass tube.
Ex. 109. Cut off the stem of a young vigorously -growing stinging nettle
in spring, and after wiping the cut surface of the stump notice with a lens
that the sap which is exuded afterwards comes from the vascular bundles
and not from the pith.
Ex. 110. Sow a few barley grains in a pot of good garden soil, and when
the plants are about 2j or 3 inches high place the pot in a warm shaded or
dark place and cover the pot with a bell glass. Notice after three or four
hours that from the tips of the young leaves drops of water are exuded.
Remove the bell-glass and leave the plants uncovered until quite dry, then
cover again and notice a further execretion of water,
CHAPTER XIV.
'CL
TRANSPIRATION : THE TRANSPIRATION-
CURRENT.
Transpiration. If the leaf of a growing sunflower or Jerusalem
artichoke is enclosed on a warm bright day in a wide test-tube
as in Fig. 85, and the end of
the tube closed with a split
cork (<r) or a plug of cotton-
wool, it will be noticed that
the inside of the tube soon
becomes covered with a dew-
like film of pure water which
gradually trickles down and
collects in considerable amount
as indicated at a.
From all parts of ordinary
land plants there is going on
a continuous invisible loss of water in the form of vapour, and
unless precautions are taken to collect the water in some manner
similar to that described above the existence of its escape from
plants into the air is not easily realized.
The exhalation of water in the form of vapour from living
plants is termed transpiration : it is not a mere physical process
of evaporation or drying such as occurs when a damp towel is
exposed to the air, but is a physiological process, which, although
influenced by external conditions, is nevertheless controlled to
some extent by the living protoplasm of the plant. Dead
191 14
FIG. 85.
TRANSPIRATION
portions of plants lose water more quickly than similar living
portions.
The amount of water transpired by a sunflower 3 \ feet high on
a warm day was found by Hales to be 20 ounces in twelve hours,
and an ordinary cabbage gave off 15 ounces in the same time.
At this rate an average crop of cabbages would give off between
3 and 4 tons of water per acre per day. As the loss by the upper
parts of the plant must be compensated by absorption of water
from t]ijs0il, it will be readily understood that land bearing a
crop is always drier than bare fallow.
If transpiration goes on at a greater rate than the absorption
by the root the turgid state of the cells is more or less decreased
and * wilting' appears. This 'wilted' condition of plants not
unfrequently happens in bright hot weather, in dry soils contain-
ing too little water, but it may occur in ordinary soils even when
the roots are actively taking in what would be a sufficient
quantity of water for the needs of the plants, if the brightness,
high temperature and other conditions encouraging excessive
transpiration were reduced.
' Wilting ' does not necessarily imply that no water is entering
the plant : it is merely an indication that the plant is losing more
than it is taking in.
Unavoidable mechanical injury to the absorbing region of the
root when plants are transplanted, injuries from the attack of
insects, and reduction of the temperature of the soil below that
at which the root is able to carry on its work satisfactorily, are
responsible for inadequate absorption of water and consequent
'wilting': moreover, an insufficient supply of air to the root
which happens when the latter is growing in water-logged soil
prevents proper absorption and may result in flagging of the
leaves of the plant
Among all kinds of plants, and especially among those species
living in dry situations, various Adaptations are observable which
tend to prevent a too rapid loss of water.
TRANSPIRATION 193
The rate at which transpiration is carried on is influenced by
the character of the external cell-walls of the various parts of the
plants.
From cells with suberised and cutinised walls the loss of water
is small, hence, from the stems and leaves of cactuses and house-
leek, from many fruits such as apples and pears, with a well-
developed cuticle, and also from stems and tubers covered with
cork-tissue and bark, the amount of transpiration is comparatively
slight : vegetable marrows, potatoes, and many kinds of apples
containing a large proportion of water, retain a large amount of
it for many weeks and even months.
The presence of a covering of woolly hairs upon the leaves
and other parts of plants aids in the prevention of excessive
transpiration, and the excretion of a waxy ' bloom ' on the exterior
of the epidermis of many leaves such as those of the cabbage,
swede and onion, and upon fruits such as plums and grapes, acts
in a similar protective manner. Experiments show that when
the ' bloom ' is rubbed from leaves and fruits a greater loss of
water takes place than from similar parts untouched.
The amount of what may be termed cuticular transpiration, or
loss through the external cell-walls of leaves, stems and parts
normally exposed to the air, is slight in all cases, except in the
youngest members whose epidermal cells have not yet become
fully cutinised.
The chief escape of water is by diastomatic transpiration, that
is by loss through the openings of the stomata, and as these are
always met with in greatest abundance upon the leaves of plants,
the latter may be considered as the chief organs of transpiration.
The cells of the spongy parenchyma of the leaf (j, Fig. 75)
possess uncutinised walls which freely allow the passage of
water-vapour into the intercellular spaces, and it is mainly from
these spaces that the vapour escapes by way of the stomata
(*)
Generally there are more stomata on the lower surfaces of
194 TRANSPIRATION
ordinary leaves and it may be shown (Expt. 114) that in such
cases transpiration is most active from the lower sides.
Unless their surfaces are specially protected by a dense
cuticle, plants with leaves of large area usually transpire and
need considerable amounts of water for proper growth : they are
frequently met with in damp situations unfavourable to trans-
piration and therefore where a large transpiring surface is a
necessity in order to get rid of surplus water.
On the other hand the leaves of plants adapted to live in dry
situations are frequently small and narrow, the transpiring surfaces
being reduced often to a minimum.
In diastomatic transpiration from a leaf or stem the opening
and closing of the aperture between the guard-cells of the stomata
(a, Fig. 74) regulates and controls the amount of water-vapour
given off, and it is the turgidity of these guard-cells which
determines whether the pore is open or shut. When the cells
are highly turgid they curve away from each other and the
opening is* as wide as possible; when they become flaccid
they straighten and the aperture between them decreases until
the free edges of the cells touch and completely close the pore.
The turgidity of the guard-cells, and therefore the possibility
of the escape of water-vapour from the leaf, is influenced both by
internal and external circumstances. About the nature of the
internal vital conditions little is known, but it may be remarked
that, when the loss of water is excessive and is not completely
compensated by absorption from the soil, the stomata begin to
close before actual ' wilting ' is observable.
The chief external conditions which influence transpiration
are:
(i) the intensity of the light to which the plant is exposed,
(ii) the water-content of the surrounding atmosphere,
(iii) the temperature of the air and soil,
(iv) the movement of the air,
(v) the water-content of the soil and the concentration and
TRANSPIRATION 195
chemical nature of the substances present in the solu-
tions absorbed by the plant.
(i) At night and in darkened rooms plants transpire very little ;
in diffuse daylight an increase is noticed, but when exposed to
bright sunlight the amount of water given off is vastly augmented.
In one of Wiesner's experiments 100 sq. cm. of leaf-surface of
a well-grown maize plant gave off in the dark 97 milligrams of
water per hour, while in diffuse daylight 114 milligrams were
lost and in bright sunlight 785 milligrams.
Usually under the influence of light the turgidity of the
guard-cells is increased, the stomatal pore therefore opens and
water-vapour is thus allowed to escape freely from the leaf.
The action of light upon transpiration is independent of the
effect of heat which usually accompanies it ; it is not, however,
simply connected with the increased opening of the stomata
under its influence, for a similar increase of transpiration is
noticed when fungi which possess no stomata are exposed to
light of increasing intensity. Light appears to act as a direct
stimulus upon the protoplasm, and under this stimulation the
latter becomes more permeable to the water of the cell-sap.
It must also be remarked that light indirectly influences
transpiration by modifying the structure of the tissues and the
composition of the cell-walls of the leaves. Plants grown in
well-exposed situations with full access to light have a greater
development of cuticle and smaller intercellular spaces within
the leaves than those grown in shaded situations; from the
former less water is transpired than from the latter.
(ii) When the air is saturated, as on a dull day or in a close
damp greenhouse, transpiration is almost entirely checked ; on the
other hand a dry atmosphere, even if cold, leads to considerable
loss of water, and the injury which occurs to delicate leaves and
other recently expanded parts of plants at low temperatures in
spring is perhaps caused as much by the dryness of the air at
such times as by its coldness.
196 TRANSPIRATION
(iii) Some plants have been found to transpire slightly at tem-
peratures below freezing-point. Increasing the temperature within
certain limits accelerates the opening of the stomata, and even
in parts of plants free from these openings transpiration is
augmented thereby.
(iv) Plants exposed to draughts and stronger currents of air lose
considerable amounts of water even when the stomata are closed.
(v) A great decrease of water within the soil in which a plant
is growing results in decreased transpiration.
The absorption of a somewhat concentrated solution also
decreases transpiration ; and plants which have taken up con-
siderable amounts of common salt transpire less than those
which have no access to this substance.
Sachs and others found that the alkalies, potash, soda and
ammonia in small quantities tended to increase transpiration,
while acids decreased it.
Ex. 111. Collect water from a leaf of a sunflower or other plant in a test-
tube arranged as in Fig. 85.
Ex. 112. (a) Take three flasks, each holding about 100 or 150 c.c., and
pour water into each until about three-quarters full.
Cut two similar branches 2 feet long from an apple tree and remove the
leaves from one of them ; place the branches in two of the separate flasks,
and after marking the level of the water in each flask with a piece of gummed
stamp paper, expose all three flasks in a well-lighted window or out of doors.
Observe the loss of water in each flask after six hours : which branch tran-
spires most ?
(&) To obtain a more accurate knowledge of the loss of water, weigh each
of the flasks and the branches separately at the commencement and the end
of the experiment. It will be observed that the water taken up by the
leafy branch is not merely absorbed into its substance but is transpired
by its leaves, for its weight at the beginning anfl end of the experiment are
nearly the same, although the weight of water lost from the flask has been
considerable.
(f) Repeat the experiment, but keep the apparatus in a dark room.
Ex. 113. Transpiration from a shoot may be demonstrated by arranging
as in Fig. 86. Push the freshly cut shoot (a) through a bored cork : it
should fit the hole in the cork tightly and should project a little way through
it. Fill the U-tube () completely with water and put the cork and shoot
TRANSPIRATION
197
into one end of the tube. See that the other end is completely full of water
and then insert into it a cork with a bent tube (). Some of the water will be
forced along the tube to a point (0), which should be marked with gummed
paper. Arrange the apparatus so that the tube b is horizontal and expose
to a bright light : the
transpiration from the
leaves of the shoot soon
causes a withdrawal of
water along the tube.
It is necessary that the
joints of the apparatus
should be air-tight and
no bubbles of air should
remain in the tube ().
Ex. 114. The differ-
ence in the transpiration
from the two surfaces of
a leaf possessing a great
many more stomata on
FlG - 86 - one side than on the other
may be shown by placing the leaf between paper which has been steeped in
cobalt chloride solution and dried.
Make a 3 per cent, solution of cobalt chloride and soak some pieces of
blotting-paper or circular filter papers in it. Allow the latter to cliyin the
air. When damp, the cobalt chloride on the paper is pink, but after drying
before a hot fire so as to drive off the small remaining amount of water, it
becomes bright blue : on absorbing a slight amount of water from the air or
from other sources it becomes pink again.
Place a leaf of a scarlet-runner between two blue dry pieces of cobalt
chloride paper, and put the whole between two sheets of glass to prevent
absorption of water from the air. After a quarter of an hour, examine the
papers and note whether that in contact with the lower or the upper side of
the leaf is pinkest.
Repeat the experiment with leaves of lilac, elder, pear, poplar, plum and
other plants.
Ex. 115. To show the influence of a covering of cork in preventing loss of
water by transpiration, take two potatoes as near the same size as possible.
Peel one of them and weigh both separately : leave them exposed to the air
for two hours and weigh again to determine which has lost most water.
Show in the same manner that when the cuticle of an apple is removed,
a much more rapid loss of water takes place than when the cuticle is
present.
198 TRANSPIRATION
Transpiration-current. The very extensive loss of water from
plants by transpiration would soon end in flagging and death if
more water were not absorbed to take the place of that which
is given off. The necessary absorption takes place at the root
in the manner previously explained and between the root-
hairs, where the water enters, and the leaves, where the bulk of
it escapes into the air, there is a continuous upward movement
of a stream of water through the root and stem of a growing
plant. This current of water is termed the transpiration-current.
By its means the necessary turgidity of the living cells in all
parts of the plant is maintained, and it is concerned with the
conveyance of a constant supply of dissolved food-materials
from the soil.
The water absorbed by the root contains dissolved in it
various substances which are essential for the nutrition of the
plant, and these substances are carried to the cells of the leaves
and other organs where they are left and utilized, only pure
water escaping in the transpiration-process. Moreover, it may
be noted that the conditions which bring about jtctive transpira-
tion and rapid movement of water, namely, a high temperature
and exposure to bright daylight, are just the conditions which
are essential for the rapid formation of organic substance from
the food-materials and for the utilisation of the food in the
nutritive processes carried on by the plant.
The movement of water in all parts of plants from cell to cell
by simple osmosis, is much too slow to be of use in maintaining
an adequate supply to the upper parts of plants where rapid
loss is occurring. The transpiration-current travels more rapidly :
in certain herbaceous plants it has been found to move at the
rate of 5 or 6 feet per hour, when the conditions for trans-
piration have been favourable; probably it is slower than this
in most trees.
The path along which the water is conducted is the wood of
the plant That it is not conveyed by the pith of a tree is clear
TRANSPIRATION-CURRENT 199
from the fact that many trees carry on their functions after the
pith is destroyed and the centre has become hollow and de-
cayed.
It can also be readily shown that the bark and bast do not
conduct the rapid upward current, for after a narrow ring-like
portion of tissues, as far as the cambium have been removed all
round a branch, the leaves above the place where the bark and
bast have been cut away do not wither.
By various experiments it has been proved that the current
travels in the youngest or outermost annual rings of woody stems
and apparently in the greatest amount, if not entirely, in the
cavities of the vessels and tracheids ; the heart-wood does not
conduct water but acts as a mechanical support
By placing the cut stems of herbaceous plants and the petioles
of leaves in coloured solutions of certain dyes, and subsequently
making sections of the stems at intervals, and by holding the
leaves up to the light, it will be observed that the solutions
have travelled along the vascular bundles which have become
stained, the rest of the tissues remaining colourless for a long
time after the bundles have been coloured.
The cause of the movement of the water through plants, or the
force which propels the transpiration-current, has been the subject
of very extensive research for more than a century.
No adequate explanation can, however, be given which will
meet all the facts of the case. The osmotic action of the living
cells of the root and stem which results in * bleeding-pressure,' and
the osmotic attraction of substances within the parenchymatous
cells of the leaves, which results in a sucking-force withdrawing
water from the vascular bundles, help to set up rapid movement
of water in a plant.
In plants of low stature, these forces depending on the activity
of living cells, may be sufficient to account for the movement of
the transpiration-current, but the conduction of water to the top
of very high trees, cannot be satisfactorily explained at present.
2OO
TRANSPIRATION
Ex. 116. (a] Dip the petiole of a leaf of elder in a weak solution of eosin
or red ink and place the whole in a blight situation. After an hour hold the
leaf up to the light and examine with the naked eye or a pocket lens ; the
solution is absorbed and travels along the vascular bundles which will be
seen to be coloured red.
Cut thin slices of the petiole and observe with a lens that the solution has
not diffused much into the tissues round the vascular bundles.
(b] Repeat the experiment with other leaves and herbaceous leafy stems.
(<:} Dip the peduncles of snowdrops, pansies, crocuses, narcissi and other
flowers in the solution and note that
the thin vascular bundles in the petals
become stained red.
Ex. 117. Remove a ring of bark,
J an inch wide^ from the branch of a
tree in summer and note that the leaves
above the cut do not wither,
Ex. 118. To show that a rapidly
transpiiing shoot possesses a consider-
able sucking-power arrange a shoot of
a sycamore, raspberry or sunflower as
in Fig. 87.
Take a piece of rubber-tube (r) about
2 inches long and slip one end on the
end of the shoot, the other on a glass
tube (a). Firmly tie the rubber-tube
to the shoot and the tube with string.
Allow the shoot to hang down, and
then pour water into the tube ; gently
tap the latter and squeeze the rubber-
tube so as to get rid of all air bubbles.
When the tube is full of water close
the end with the thumb, turn up the
apparatus into the position indicated in
the Fig, 87, and place the end of the
fir tube below the water (n) and mercury
J/fc- (6) in the glass dish. Support the shoot
21P?fr by means of the clip and expose the
whole in a bright window. The water
in the tube is transpired by the leaves of
FIG. 87.
the shoot, and a considerable amount of the mercury is lifted into the tube,
as shown at (A 1 ).
CHAPTER XV.
THE ABSORPTION OF FOOD-MATERIALS.
i. Food and food-materials. The protoplasm or the living
material within actively growing plants and animals is continu-
ally undergoing chemical changes which result in its destruction
and the formation from it of simpler compounds. To repair its
waste and to enable it to carry on the work of constructing new
parts, food is necessary.
The nature of the/<ra/ of a plant, or the substances which are
utilised by the protoplasm for the formation of new organs and foi
its own nutrition, is mot readily understood after a consideration
of the materials which are consumed during the growth of an
embryo plant from a seed.
The substances stored by the parent in the endosperm or within
the tissues of the embryo for the nutrition of the latter are chiefly
complex organic compounds such as starch, fats, and proteids,
and it is these substances, or very slightly altered forms of them,
which are consumed in the processes of nutrition and growth
which occur when germination commences.
Similarly, the substances upon which the young shoots of a
sprouting potato tuber or the young leaves and flowering shoots
of a growing bulb are fed, are carbohydrates, fats, and proteids
or organic compounds of analogous complex constitution.
The developing buds of a tree in spring are also nourished by
similar compounds, and there is every reason to conclude that
the protoplasm in plants and animals alike, depends at all
times for its immediate nutrition upon organic materials of this
character.
801
202 ABSORPTION OF FOOD-MATERIALS
Animals and parasitic and saprophytic plants obtain these
compounds directly or indirectly from the bodies of other living
or dead organisms, and without a supply of such substances they
soon die. Green plants likewise need food of a similar complex
nature for development and growth ; they are, however, not
generally adapted to obtain compounds of this character from
their surroundings, but are able to manufacture them from
inorganic compounds such as carbon dioxide, water, and various
salts which they derive from the atmosphere and the soil.
Although these simple inorganic materials absorbed from the
air and the soil are frequently spoken of as the food of plants,
it is better perhaps to speak of them as food-materials , for the
living substance of a plant cannot directly nourish itself upon
them. It is only after they have been elaborated or built up
into more complex compounds that they become food which
can be used for the nutrition of the protoplasm and the formation
of the tissues of growing organs.
A seedling after it has consumed the food stored for its use
by its parent, is unable to make use of carbon dioxide and simple
salts supplied to it until it is exposed to light under certain
conditions which allow it to elaborate and synthetically build up
from these inorganic materials compounds similar to those
which it has already consumed, and which were supplied ai>d
manufactured previously by its parent.
2. Food-materials and their absorption. The food-materials
absorbed by ordinary green plants are derived from the sur-
rounding atmosphere and soil upon which the plants grow.
By the methods of sand-culture and water-culture it has been
proved that for complete and perfect nutrition, green plants
must be supplied with food-materials which contain collectively
some ten or eleven elements as explained in chapter xii.
It has also been determined by the same experimental
methods that plants are by no means indifferent as to the form
in which any particular element is presented to them. For
FOOD-MATERIALS AND THEIR ABSORPTION 203
example, they are not able to utilise all nitrogenous compounds
as sources of nitrogen, nor are they able to obtain their necessary
carbon from all kinds of carbon-compounds.
A compound to be of service as a food-material capable of
supplying a particular element for the nutrition of a plant, must
(i) be soluble and able to diffuse through the cell-wall and proto-
plasm of the cells, and (ii) must also possess a certain chemical
structure.
The carbon dioxide gas present in the air is the chief source
from which the carbon is obtained ; the absorption and subse-
quent use of the gas is discussed in the succeeding chapter.
The food-materials furnishing the rest of the elements needed
by plants are obtained from the soil by osmosis through the
root-hairs. Before they can enter the latter they must be in
solution, since no solid particle however small is able to
pass through the closed cell-rnembranes of the absorbent
hairs.
Moreover it is only from weak solutions of food-materials that
plants can absorb what they need ; plants grown by the
method of water-culture make the most satisfactory progress
when the total amount of solids dissolved in the water does not
exceed from *2 to *5 per cent, or 2 to 5 parts in 1000 of water.
Solutions containing 2 or 2\ per cent, of dissolved substances
act injuriously upon the protoplasm of the plant, and prevent
growth : hence the importance of avoiding readily soluble
manures in excess.
The water of the soil from which plants obtain all they need
usually contains not more than *oi to '03 per cent, of solid
matter dissolved in it
Carbon dioxide gas is produced within the soil in the processes
of putrefaction and decay of the manures present, and is excreted
to a slight extent in the respiration process carried on by the
protoplasm of the root-hairs. This gas indirectly assists plants
to absorb useful food-materials, for some of the latter which are
204 ABSORPTION OF FOOD-MATERIALS
insoluble in pure water, dissolve appreciably in water containing
carbon dioxide.
It must also be noted that carbon dioxide, potassium hydrogen
phosphate and other substances possessing an acid reaction
permeate the cell-walls of the root-hairs, and enable the latter
to corrode and dissolve certain mineral compounds such as
calcium phosphate and the carbonates of calcium and magnesium
with which they come into contact.
3. When the roots of a plant are immersed in a vessel of water
containing a substance in solution, the dissolved substance may
not be able to pass through the cell-wall or the cytoplasm of the
root-hairs in which case none enters the plant. If, however, the
substance can diffuse through both cell-membranes, it will pass
into the root-hairs and from there into the rest of the cells ot
the plant until the cell-sap contains the same proportion of it
as the water outside the plant ; when this condition is reached,
equilibrium is established and no more of the dissolved material
is absorbed. Should the substance after entering the plant be
used up in the processes of nutrition, or changed into an insoluble
or non-diosmosing compound, the osmotic equilibrium in regard to
this particular material is destroyed, and more of it can then enter.
In this manner a plant is able to completely extract the whole
of a substance dissolved in water to which its roots have access,
and can accumulate within itself large amounts of certain elements
from solutions containing the merest traces of them. For example,
sea-water contains not more than one part of iodine in 100 millions
of water, and yet certain sea-weeds accumulate such quantities
that from i to 3 per cent, of their ash consists of this element.
The total amount of any particular element occurring in the
ash of a plant is dependent (i) upon the amount of the soluble
material containing it present in the soil upon which the plant
is growing; (2) upon the peculiar specific permeability of the
protoplasm of the root-hairs ; and (3) also upon the question
of whether the plant utilises, transforms or removes the par-
FOOD-MATERIALS AND THEIR ABSORPTION 205
ticular material from its cell-sap so that more can enter by
osmosis.
Two different species of plants growing in the same nutrient-
solution or with their roots in the same soil are generally found
to contain very different amounts of each of the various a*sh-
constituents. For example, the amount of silica in the ash of
the white water-lily is generally less than a per cent., while that
of the common reed (Phragmitcs communis Trin.) growing on the
same marshy soil contains more than 70 per cent, of silica ; and
while the ash of pea plants is found to contain not more than
about 7 per cent, of this substance, that of grasses growing on
the same soil contains over 20 per cent, of it.
This different quantitive selective power is chiefly due to the
difference in the power of making use of silica by the two species
of plants compared; the substance from which the silica is
derived probably diffuses with equal freedom through the cell-
walls of both, but whereas the reed continually removes the
compound from the cell-sap and deposits large quantities of
silica in its cell- walls thus allowing more to flow in, the water-
lily uses very little and a state of osmotic equilibrium is soon
reached, after which no more enters the plant.
The amount of any particular substance absorbed from the
soil by a plant is in direct proportion to the amount used in the
chemical processes carried on by the plant, so that a substance
present in abundance may be absorbed in very minute quantities
only, whereas a compound present in small amount may be
completely extracted from the soil.
4. The nature of the various inorganic compounds from which
green plants obtain their supply of the elements essential for
complete nutrition, has already been mentioned in discussing
the composition of plants in chapter xii.
Practically all these food-materials except carbon are absorbed
from the soil.
Experience proves that the continuous growth and removal
206 ABSORPTION OF FOOD-MATERIALS
of crops from the land end sooner or later in reducing such
land to a state in which it refuses to grow a remunerative crop
of any kind unless manures are applied to it.
This more or less barren condition of land from which many
crops have been removed is explained by the fact that plants
lift into their bodies from the soil on which they grow a certain
amount of its constituents, and the removal of a crop therefore
means the removal of a considerable weight of the most im-
portant components of the soil : since the latter does not in
any case contain an unlimited supply of these plant food-
materials in a soluble and available form, it will be readily
understood that the continuous removal of crops from a field
must eventually lead to exhaustion, and that plants grown upon
it would starve, unless a new supply of food-material is added
to take the place of that previously removed.
It is true that the soil under such treatment does not become
so completely exhausted of its useful constituents that plants
altogether refuse to grow upon it, for soluble food-materials
are constantly being released or renewed from the store of
insoluble material composing the soil by the disintegrating
influence of frost and heat, and the chemical action of the
air and water upon it. Nevertheless, in this country, for the
production of a remunerative crop, the direct application of
manure containing food-materials or from which the latter can
be readily set free, is necessary in the case of most soils from
which two or three successive crops have been taken.
Plants cannot grow unless they are supplied with all the
elements mentioned as essential on pp. 171 to 175 ; should one of
these be totally missing from the soil, growth becomes impossible.
From this peculiarity the power of the soil to yield a crop is
controlled by the essential element which is present in the least
amount.
If a soil contains too small an amount of phosphates
for the growth of a crop, the fact that elements such as
FOOD-MATERIALS AND THEIR ABSORPTION 207
nitrogen or potassium are present in great abundance avails
nothing, for these cannot be utilised until the necessary phos-
phates are available.
The food-materials from which plants obtain the sulphur, iron,
magnesium, calcium, carbon, hydrogen and oxygen are almost
always present in the soil and air in sufficient abundance for the
needs of all crops, but the compounds which yield nitrogen,
phosphorus and potassium are generally removed in such
quantities that the supply is soon reduced to such a point that
for full crops manure containing one or all of these elements
must be added to the soil.
CHAPTER XVI.
CARBON-FIXATION; 'ASSIMILATION; OR
'PHOTOSYNTHESIS/
i. THE source from which plants obtain the large quantity of
carbon of which more than half their dry weight consists, has
been the subject of extensive investigation for a long time.
Parasitic plants, such as dodder, broom-rape and many fungi,
attach themselves to other living organisms and absorb the
carbon they need in the form of sugar, proteids and other
elaborated carbon compounds from their victims. Saprophytes,
such as the bird's-nest orchis (Neottia\ mushrooms, and the
majority of common fungi, which like the above-mentioned
parasites are devoid of chloroplasts, obtain their carbon in a
similar elaborated form from the carbon compounds present in
the remains of dead plants and animals upon which they grow.
It is probable also that all green plants absorb and utilise
organic carbon compounds from the humus or decaying vegetable
and animal remains within the soil, although it has been proved
that this source is insufficient to supply all the carbon needed
for the perfect healthy nutrition of plants of this kind.
By the method of water-culture or sand-culture it may be
readily shown that ordinary green plants flourish and increase
in carbon-content when their roots are supplied with a solution
of food-materials containing no carbon, so long as the solution
contains all other essential elements.
Under these circumstances the only source of carbon is the
carbon dioxide of the atmosphere surrounding the leaves, and
although the proportional amount of this gas present in the
203
1 ASSIMILATION/ OR ' PHOTOSYNTHESIS ' 209
air is very small, averaging about 2*8 parts in 10,000, it is from
this source that the whole of the carbon of plants grown by the
method of water-culture is derived.
In the processes of fermentation and decay going on in
ordinary soil carbon dioxide is produced and the air permeating
the interstices of the soil may contain as much as 5 per cent, of
this gas, some of which enters the roots of plants dissolved in
the water of the transpiration-current : it has, however, been
shown by Cailletet and Moll's experiments that the supply
of carbon dioxide obtained in this manner is insufficient for the
requirements of ordinary green plants.
Extended and carefully-conducted investigations have proved
beyond doubt that the chief food-material utilized by green
plants for their carbon-supply, is the carbon dioxide of the air,
and that this gas is absorbed by means of the leaves. Moreover,
it is through the stomata that the gas enters into the tissues
and only in slight degree, if at all, through the cuticle of
the epidermal cells.
The rate at which the absorption of the gas is carried on
by the leaves has been investigated by Brown and Escombe :
the amount absorbed by a sunflower exposed to diffuse daylight
was found, in one instance, to be 412 cubic centimetres per
square metre of leaf-surface per hour ; the hourly absorption for
a Catalpa leaf was 345 c.c. for each square metre. Under
favourable conditions the rate of absorption of the gas by a leaf
was found to be equal to one-half that of a strong solution of
caustic potash of equal area, and, since the actual openings
between the guard-cells of the stomata in the leaf investigated
amounted to not more than yj^ part of ttoe whole area of the
leaf, it follows that the rate at which carbon dioxide entered
was fifty times as rapid as that at which the gas is absorbed by a
solution of catfstic potash, a truly astonishing result.
This absorptive activity on the part of green vegetation would
soon result in the total removal of carbon dioxide from the air,
210 'CARBON-FIXATION,' 4 ASSIMILATION
were it not for the fact that the atmosphere is being continually
replenished with carbon dioxide which is produced in the
process of respiration carried on by all living things, and by the
combustion of coal, wood and other kinds of fuel containing
carbon.
After entering into the cells of the leaf the carbon dioxide,
together with a certain proportion of water, undergo chemical
changes which result in the formation of soluble carbohydrates,
oxygen being also set free during the process.
The carbon of the carbon dioxide thus beconres * fixed, 1 and
a rapid accumulation of carbohydrates takes place in the tissues
of the plant, the oxygen escaping into the air.
The process may be represented thus :
carbon dioxide + water = a carbohydrate -f oxygen.
It has been customary among botanists to use the term
assimilation for the synthesis of carbohydrates by green plants in
this manner from carbon dioxide and water, but it would be
better to reserve the term for the conversion of foods into the
substance of the tissues, as is done by animal physiologists, and
employ another for this synthetical production of carbohydrates
which is peculiar to green plants. As the operation is dependent
upon light the term photosynthesis has been suggested and some
such term or the expression ' carbon-fixation* is much to be
recommended instead of ' assimilation. 1
The exact nature of the carbohydrate first formed during the
process is not known. Von Baeyer suggested that formaldehyde
(CH 8 O) is first produced according to the equation
CO 2 + H 2 O = CH 2 O + O 2 ,
and that this compound subsequently undergoes condensation
into a carbohydrate of the formula C 6 H 12 O 6 . However, formal-
dehyde cannot be detected in the tissues in which the process
of ' carbon-fixation ' is going on, and although Bflkorny's experi-
ments show that under certain conditions formaldehyde can be
utilised by plants for the production of carbohydrates, the view
OR 'PHOTOSYNTHESIS' 211
that this compound is the first step in the formation of carbon
compounds from carbon dioxide and water is nothing more than
a hypothesis.
What is certain is that sugars are soon formed in the
cells of the leaf-parenchyma after the green leaves of plants
absorb carbon dioxide from the air, and the investigations
of Brown and Morris point to the conclusion that cane-sugar
is the first sugar to be manufactured, and that subsequently
dextrose, levulose and maltose sugars make their appearance in
leaves in consequence of the action of enzymes upon the
previously-formed cane-sugar and starch.
In a great many plants when the accumulation of sugar within
the cells of the leaves reaches a certain point the chloroplasts
form starch-grains from it; the starch-grains appear within the
substance of the chloroplasts and are the first visible products of
* carbon-fixation.'
The total amount of carbohydrates produced by leaves of
the same area depends upon internal vital peculiarities of the
different species of plants ; for example, in a given time a
sunflower leaf produces more than a leaf of a dwarf-bean of the
same area. The amount manufactured by a sunflower during
twelve hours on a moderately bright day was found by Brown and
Morris in one instance to be a little more than 12 grams of
carbohydrates per square metre of leaf-surface.
2. The manufacture or synthesis of carbohydrates in the
manner indicated above is dependent upon various conditions,
of which the following are the most important :
(i) The plants must be living.
(ii) Carbon dioxide must be present in the air surrounding
their leaves.
(Hi) The leaves must contain chloroplasts.
(iv) A certain intensity of light is essential, and
(v) an adequate degree of temperature is necessary for the
process.
212 ' CARBON-FIXATION/ ' ASSIMILATION '
(vi) ' Carbon-fixation ' is also influenced by the presence or
absence of certain mineral substances, especially compounds of
potassium obtained from the soil, but the particular part which
these substances play in the process is not known.
' Carbon-fixation ' is a vital process and ceases with the death
of the plant.
Plants grown in air from which the carbon dioxide has been
extracted do not increase in dry weight, and after a time death
takes place from starvation. They are not able to live in an
atmosphere of pure carbon dioxide, but are able to carry on
* carbon-fixation ' in air containing as much as 20 or 30 per cent,
of the gas. According to the experiments of Montemartini the
formation of carbohydrates is carried on best and most rapidly
in air containing 4 per cent, of carbon dioxide, an amount six
or seven times as great as that normally present in the atmosphere.
* Carbon-fixation ' is apparently carried on only by specialised
portions of the protoplasm of the cells, namely, by the chloro-
plasts, for it only occurs in the leaves and parts which are green.
The roots, the petals of flowers, and the white portions of
variegated leaves from which chloroplasts are absent take no
part in the process, and parasitic and saprophytic plants which
are devoid of these structures are also incapable of utilising
carbon dioxide for the formation or synthesis of carbohydrates.
The leaves of the copper-beech, purple cabbage, red beet
and many other plants have reddish cell-sap which disguises the
green colour of the chloroplasts : the latter are nevertheless
abundant in the palisade and spongy parenchyma of such leaves,
and the plants as readily carry on the process of 'carbon-
fixation ' as those having ordinary green leaves.
The chloroplasts are small structures imbedded in the cyto-
plasm of the cell; their substance is permeated with a green
pigment named chlorophyll, associated with which is a reddish
orange substance known as carotin^ and a yellow material
termed xanthophyll allied to the latter.
OR ' PHOTOSYNTHESIS 213
The chemical nature of chlorophyll is unknown : its production
is, however, in some way dependent upon the presence of iron
in plants although it does not appear to contain this element.
The chloroplasts of plants grown in the dark or covered up for
a time, lose their green colour and become colourless or pale
yellow. With the exception of the chlorophyll of the chloroplasts
present in the embryos of certain plants, the production of this
green pigment is dependent upon light : the cotyledons and first
leaves of most seedlings and the leaves from underground buds of
perennial plants only become green when they reach the surface
of the soil. Moreover, the formation of chlorophyll is influenced
by heat ; the plastids (see p. 107) of many plants grown in the
dark do not develop a green tint even when exposed to light
when the temperature is below freezing-point, but do so at
higher temperatures.
Chlorophyll, perhaps in a more or less altered form, can be
extracted by means of alcohol : its solutions are fluorescent,
appearing blood-red when seen by reflected light, and green
when viewed by transmitted light. When acted upon by acids
it changes to a dirty brownish-green colour. After death of
the cytoplasm of the cells, the acid cell-sap, which is confined
within the vacuole of the cells when the plant is living, diffuses
through the cytoplasm to the chloroplasts, causing them to
change to the brownish-green tint so characteristic of dead leaves.
Light is not only essential for the formation of chlorophyll,
but it is also directly necessary for the process of 'carbon-
fixation,' as it is from the energy of the sun's rays that the
energy required to effect the decomposition of the carbon
dioxide and water used in the process is derived.
In darkness, green plants are unable to effect the synthesis of
carbohydrates from carbon dioxide and water, and under such
conditions they decrease in dry weight owing to the loss caused
by respiration, which goes on at all times (see chap. xix.).
In shady places, in badly-lighted rooms, and in greenhouses
214 'CARBON-FIXATION/ 'ASSIMILATION*
during the dull days of winter, the manufacture of carbon com-
pounds is usually slow, and is often insufficient to supply the
proper needs of plants. Similar partial starvation due to want
of light occurs among thickly-planted crops and in the inner
boughs of trees bearing an excess of leaves, and in all cases of
over-crowded plants. With an increased intensity of light,
'carbon-fixation' increases proportionally up to a maximum,
which for many plants is not attained until they are exposed
to direct sunlight.
Certain shade-loving plants, however, need only a moderate
intensity of light for proper nutrition ; exposure to intense
light retards or altogether suspends their activity in this respect,
and at the same time acts injuriously upon their chloroplasts
and other protoplasmic cell-contents.
In the majority of plants, the epidermal cells are free from
chloroplasts, and the cell-contents of this tissue no doubt screen
the chloroplasts of the deeper-lying tissues from the deleterious
action of too brilliant light. Moreover, the chloroplasts are
moved into more advantageous positions within the cells, when
the intensity of the light falling upon the leaves becomes too
great.
The red, orange and yellow rays present in sunlight are most
effective in promoting ' carbon-fixation/ the purple and violet
rays having very little effect upon the process.
In many plants * carbon-fixation ' goes on to a slight extent
at one or two degrees above freezing-point : with increasing
temperature the process increases in activity up to about 20* or
25* C., beyond which temperatures it decreases until at about
56 C. it ceases altogether with the death of the plant.
Ex. 119. Place some shoots of Potamogeton^ Ehdea canadensts, mare's tail
(Hippuris) or mint in a beaker full of well water. Slide a glass funnel into
the beaker as indicated in Fig. 88, and over the end of the funnel place a test*
tube full of water. Expose the whole to bright daylight, and notice that
bubbles of gas rise from the leaves of the plants and collect at o in the test-tube.
After a few c.c. of gas have been collected, remove the test-tube, and
OR 'PHOTOSYNTHESIS
215
O
place the thumb over the open end of the tube while it is below water, so
as to prevent air from getting in. Take out the tube completely, turn it
up, and keep the thumb over the end of the tube all the time ; then
remove the thumb, and plunge a smouldering match-stalk into the gas.
Although the gas collected is not pure oxygen,
it contains a considerable proportion of the latter,
and causes a smouldering match to burst into
flame when placed in it.
Ex. 120. (i) Tie a terminal shoot of Elodea
4 to 6 inches long to a glass rod, and place so
that the broken end of the shoot is uppermost
in a tall glass cylinder full of well water.
Expose the whole to bright daylight ; notice
and count the number of bubbles of oxygen which
rise from the broken end of the shoot in two or
three minutes.
(ii) Move the apparatus to a badly-lighted
room, and count the bubbles rising in the same
time as before. Do more bubbles rise when the
plant is exposed to bright light than when exposed
to a dim light ?
Ex. 121. Repeat the above experiment, using
boiled water from which all the carbon dioxide
has been driven off. Notice that little or no gas
is evolved. Now supply carbon dioxide to the
water by blowing through a glass tube into it.
FIG.
Ex. 122. Repeat Ex. 119, using roots, flowers, or other portions of plants
which are not green, to show that oxygen is not evolved from such parts.
Ex. 123. (i) In the afternoon of a warm, bright day pluck off a leaf from
several common broad-leaved plants, and test for starch in them, thus :
First place them in boiling water for a minute, after which transfer them
to a vessel containing warm methylated spirits to dissolve out the chlorophyll
and other pigments. Leave them in the latter for a few hours until they are
pale in colour, and then transfer them to a saucer containing a solution of
iodine (see Ex. 85).
If they contain starch they will turn black or deep purple.
(ii) Test for starch in leaves variegated with white patches and show that
none is formed in the white parts from which chloroplasts are absent.
Ex. 124. (i) Smear one half of a pear or poplar leaf with cacao butter or
best lard on both sides to block up the stomata. Leave for two days, and
in the afternoon of the following day, test the whole leaf for starch, after
removing the butter with hot water.
216 4 CARBON-FIXATION '
Note that no starch is formed in the half to which access of carbon dioxide
is prevented.
(ii) Smear the upper surface only of a pear or poplar leaf, and the lower
surface only of another similar leaf. Leave for three days as before, and then
test for starch.
Find out which leaf possesses most starch ; then determine with micro-
scope on which surface stomata are most abundant.
Ex. 125. To show the effect of darkness on starch formation, tie up a leaf
of Tropaolum in a thick brown -paper bag so that no light can get at it.
Leave it covered up for two days, and then test for starch.
Ex. 126. Boil a quantity of young grass leaves for a minute or two and
then extract the chlorophyll by placing the leaves in strong alcohol in a
dark cupboard.
Pour some of the solution into a beaker or large test-tube ; note the green
colour when held up to the light, and dark red colour when viewed by
light reflected from it.
Note the effect on the colour when a few drops of hydrochloric acid are
added to the solution.
Ex. 127. Grow some seedlings of wheat, mustard, or peas in total dark-
ness, and note that the leaves are not green. Expose the plants to light
and observe when the first signs of a green colour are visible.
Ex. 128. Place a large can, bowl or basin upside down on a lawn or
grassy field so as to exclude light from the plants beneath it. Leave it for
one or two weeks and then examine the grass beneath ; note the loss of
green colour.
CHAPTER XVII.
FORMATION OP PROTEINS. TRANSLOCATION
AND STORAGE OF FOODS.
i. WITHIN the body of a living plant a great variety of chemical
changes, which are collectively referred to as metabolic processes
or metabolism, are always being carried on. Some of these
changes, like those discussed in the preceding chapter, result in
the formation of complex compounds from simpler ones; such
constructive chemical processes are spoken of as anabolism^
the destructive chemical changes, such as those involved in
the respiration-process, which result in the breaking down or
decomposition of complex compounds into simpler ones, being
included in the term catabolism.
The conditions under which the chemical reactions take place
within a living plant, are very much more complicated and
probably of a very different class from those met with in a
chemical laboratory, and our knowledge respecting the chemical
changes involved in the production of the many different organic
compounds present in plants is still very scanty and imperfect,
2. Formation of proteins. During the growth of green plants
there is not only the synthesis or construction of sugars and
other carbohydrates from simple inorganic food-materials, but
other organic compounds are built up, the chief of which are
those containing nitrogen, namely, amides and proteins.
The natural sources from which green plants obtain the
nitrogen necessary for the production of these compound*
are:
(i) The free uncombined nitrogen of the atmosphere.
217
218 FORMATION OF PROTEINS
(ii) The complex nitrogenous organic compounds of the humus
in the soil.
(iii) The ammonium salts, and
(iv) Nitrates also present in the soil.
Among the higher plants only the Leguminosae appear to be
able to utilise the free nitrogen of the air (see p. 806), and it has
been proved by means of sand- and water-cultures that although
green plants are able to make immediate use of ammonium salts
and a great variety of organic nitrogenous compounds, such as
urea and leucine, they nevertheless thrive best when supplied
with nitrogen in the form of nitrates ; this is true even of
leguminous plants, which can, under certain conditions, obtain
nitrogen from the atmosphere.
As ammonium salts and the nitrogenous organic compounds
of dung, urine and humus when placed in the soil are ultimately
changed into nitrates (see p. 799), it is inferred that crops
ordinarily obtain the chief portion of the nitrogen which they
need from the nitrates of calcium, magnesium, potassium and
sodium present in the soil.
The chemical changes which nitrates undergo after their absorp-
tion by plants and in what tissues or organs these changes take
place are still practically unknown.
Plants differ very much in regard to the method of taking up
and utilising nitrates ; in some species nitrates can be detected
in all parts of the plants, while in others they can only be found
in the stem or roots, and in some none are found, in which latter
case the decomposition of these compounds appears to take place
at the very threshold of entry into the plant, namely, in the root-
hairs and delicate fibrils of the root.
It may safely be concluded that between the simple nitrates
absorbed from the soil, and the proteins produced in the plant,
there are many intermediate products manufactured. What
these products arc is not known with certainty, but there is
no doubt that asparagine (amido-succinamic acid) and probably
TRANSLOCATION AND STORAGE OF FOODS 219
other amides and amido-acids are among the intermediate nitro-
genous compounds from which proteins are ultimately con-
structed with the aid of previously-formed carbohydrates.
The construction of proteins from asparagine and sugars appears
in certain cases, to take place in the leaves and may go on in
the dark, but in some instances the process is favourably in-
creased when the plants are exposed to the light. Similar
manufacture of proteins occurs in roots and probably in other
parts of plants.
Schultze and others have shown that plants can utilize nitrates
and ammonium salts for the manufacture of asparagine and allied
amido-compounds. According to Suzuki, the conditions for
the formation of asparagine from nitrates are a somewhat high
temperature and the presence of sugar.
Besides being produced synthetically from absorbed nitrates or
ammonium salts and sugars, asparagine is apparently produced in
plants by the decomposition of proteins, and this asparagine can
be utilised again for the regeneration of proteins when a suitable
supply of carbohydrates is present to complete the synthesis.
In addition to nitrates, other inorganic compounds such as
sulphates and phosphates take a part in the formation of proteins,
for the latter contain sulphur and sometimes phosphorus as well ;
probably some of the metallic elements, such as potassium and
calcium, which are known to be essential for proper nutrition
of plants, are also more or less directly indispensable to the
formation of complex proteins.
3. Utilisation, translocation and storage of plant-foods.
The various organic compounds manufactured by anabolic
processes are utilised in different ways. A certain amount of
sugars and fats are consumed in the respiration-process, and in
the case of plants grown in the dark and in the earliest stages of
the growth of seeds, tubers and bulbs, the destructive respiratory
process results in a considerable loss of carbon which is given
off as carbon dioxide into the air ; under such conditions there
220 FORMATION OF PROTEINS
is therefore a decrease in the dry weight of the plants. However,
when the leaves and organs which effect * carbon-fixation ' have
been developed, there is usually a continuous increase in dry
weight from the beginning to the end of the life of a plant,
anabolism being largely in excess of catabolism.
The larger proportion of the sugars, fats, proteins and other
organic compounds manufactured by the plant, are employed in
the construction of the cell-walls and protoplasm of the new cells
arising at the growing points, and in nourishing the protoplasm
of more mature cells and also in thickening the walls of the latter.
Under ordinary conditions of growth more organic material is
constructed than is needed for the immediate nutritive require-
ments of the individual plant : the excess is stored for the
nutrition of its offspring, and, in the case of a perennial, for
its own nutrition at subsequent periods of its growth.
According to Brown and Morris' researches cane-sugar appears
to be the first sugar formed in the 4 carbon-fixation ' process
carried on by green leaves.
The cane-sugar appears to be subsequently transformed by the
enzyme invertase in the leaves into dextrose and levulose ; the
latter sugars then travel from the leaf-blade through the petiole
and into the stem along which they are translocated to the buds,
growing-points and other parts of the root and shoot where
growth and the formation of new organs or new tissues are
taking place, and also to the centres, where storage of reserve-
foods is occurring.
The starch formed in the chloroplasts of the leaf-blade, is
acted on by the enzyme diastase present in the cells and
becomes transformed into maltose which travels from the leaf
with the rest of the sugars to the centres of nutrition and
storage.
Diastase increases in leaves kept in the dark, and in con-
sequence the disappearance of starch goes on most rapidly at
night
TRANSLOCATION AND STORAGE OF FOODS 221
The sugars and other soluble carbohydrates travel in the
plant osmotically from cell to cell, by far the largest amount
being transferred from the leaves to the stem through the bast
and elongated parenchymatous cells surrounding the vascular
bundles \ in the stem and roots these compounds travel through
the tissues of the bast and probably to a slight extent through
the inner parts of the cortex also.
The medullary rays receive from the bast the materials
manufactured in the leaves, and convey them to the cambium
and living portions of the wood needing nourishment.
Proteins, which diffuse very slowly or not at all through cell-
walls, are transferred long distances in stems and roots through
the open sieve-tubes of the bast. These compounds are also
frequently acted upon by enzymes which decompose them into
peptones and the amides, asparagine, leucine and tyrosine, which
diffuse with greater ease.
The stream of sap conveying crude food-materials from the
soil to the leaves travels through the wood, but the elaborated
foods are translocated chiefly through the bast.
The removal of a complete ring of * bark ' from the stem of a
tree as far as the wood-tissue does not interfere with the
upward flow of water and food-materials, but it prevents the
stream of elaborated food from passing down to the roots, and
unless the wound is healed by the formation of new conducting-
tissue across the exposed part, the roots ultimately die of
starvation and the whole tree succumbs. The time during
which a tree will live after being * ringed ' depends upon the
kind of tree and also upon the amount of organic material
stored in the root-stock and roots before the wound was made.
' Ringed ' trees may, however, live an indefinite period if
adventitious shoots arise below the ' ringed ' part, for these
leafy shoots manufacture organic material and as there is an
uninterrupted connection between such new shoots and the
root-system, the latter can receive a certain amount of nutrient
222 FORMATION OF PROTEINS
material which may be sufficient to enable it to grow for a long
time.
The substances manufactured in a shoot or branch of a tree
are prevented from leaving it when the branch is ' ringed,' and
the shoot and fruits upon it grow more luxuriantly in consequence
of their increased food-supply.
There is often a special growth of the wood and bast tissues
just above the ' ringed ' part in consequence of the accumulation
and utilisation of organic material at that point.
Similar thickening or enlargement of the stem arising from
impeded flow of elaborated sap is seen immediately above the
point where scions have been inserted on stocks in the grafting
process, especially where the union of the two grafted parts is
imperfect.
Wire or string tightly bound round the stems and branches of
trees leads to similar results.
Ex. 129. Remove leaves from tropseolum, clover, and other plants in the
afternoon and test for starch in them with iodine as in Ex. 123. Remove
from the same plants similar leaves in the early morning of next day and
test for starch.
Compare the two sets of leaves and note the greater amount of starch in
those plucked in the evening
Ex. 130. Remove in spring or early summer a ring of bark about half an
inch wide from the branches of several kinds of trees. Also from some of
the branches remove two or three similar rings of bark near each other, so as
to leave a bud on some of the unringed portions and no buds on others.
Note the subsequent growth and development of the various parts of the
shoots above and below the ' ring/ Do the buds lying between two ' rings'
develop satisfactorily ?
Ex. 131. In spring before the leaf-buds are open make cuttings of the
willow about a foot long from well-ripened portions of last season's shoots :
'ring' the cuttings about one and a half inches from their base and place
some in water and others in damp soil. Leave them until adventitious roots
develop ; note the relative size and rate of development of the roots and
buds above and below the ' ringed ' part.
Bx. 133. Tightly bind string or wire twice or three times round the branch
of a tree, and observe the subsequent development of the various organs above
and below the bound part.
TRANSLOCATION AND STORAGE OF FOODS 223
4. The surplus organic material manufactured by a plant is
transferred to various parts of its body to be stored for future
use. Among annuals the reserve-food is accumulated only in
the seeds ; in wheat and other cereals the endosperm of the
seed becomes gradually filled with it, while in peas, beans and
many annuals the reserve is stored in the cotyledons of the
embryo.
Among biennials and perennials, the seeds are similarly stored
with reserve-food; but such plants, before the end of one
growing-season, accumulate and store a considerable quantity of
organic material in their vegetative organs, which material serves
for the nutrition and growth of the cambium, buds and roots
during the earlier part of the succeeding season.
In turnips, carrots and mangel the reserve-material is stored
in the roots : in onions and tulips it is accumulated in the leaves
of the bulbs, in potatoes in the tubers, while in hops and many
herbaceous perennials it is hoarded in the rhizomes or rootstocks.
Trees and shrubs store their reserve-material chiefly in the
parenchyma of the cortex and medullary rays in the stems.
In the onion and many bulbs the carbohydrate reserve is
stored chiefly in the form of dextrose, while many fruits store
levulose also in their cell-sap.
In the sugar-cane, sugar-beet, turnip and other roots the
reserve is cane-sugar dissolved in the cell-sap ; in the tubers of
the Jerusalem artichoke inulin takes the place of sugar. In
the majority of plants the reserve-materials are chiefly stored in
a solid insoluble form, in which state they take up less space than
they would do in solution.
The commonest solid carbohydrate reserve-material is starch
which occurs in the form of small grains previously described
(p. 156). In some instances very minute particles of starch are
temporarily formed within the cytoplasm but the largei starch-
grains present in the special storage centres are produced by the
leucoplasts (see p. 108) of the cells from sugars which are trans-
224 FORMATION OF PROTEINS
ferred to them from the leaves where 'carbon-fixation' is going
on. Thus, the starch in the cereal grains, in the tubers of
potatoes, and in the medullary rays and cortex of trees in winter,
is formed from sugars primarily manufactured in the leaves.
Starch-grains formed by the leucoplasts are usually much
larger than those temporarily formed and stored in the allied
chloroplasts of the leaves.
In certain seeds some of the carbohydrate reserve is stored in
the form of thickened cell- walls consisting of hemicellulose.
The fats and fixed oils occurring in the seeds of flax, cotton,
and rape are non-nitrogenous reserve-materials, which are first
visible in the form of minute drops in the protoplasm ; the
small drops run together ultimately and form larger drops. In
some cases the fats and oils appear to be manufactured from
dextrose and other sugars, while in others they arise by the
conversion of starch.
Asparagine, leucine, glutamine, and other amido-compounds
frequently form the chief store of nitrogenous materials present
in the cell-sap of tubers, roots and rhizomes of plants. With
increasing maturity of the root or tuber some of these
compounds are converted into proteids. In most ripe seeds
the nitrogenous reserve-material consists almost entirely of
proteins stored in the form of solid aleuron-grains and other
more or less amorphous masses : only a small proportion of
amido-compounds are present.
It will be observed that the substances actually stored are
usually different in chemical constitution and solubility from the
organic materials transported into the cells where the storage is
proceeding. One form of sugar is changed into another after
entering into the cell or is utilised by the leucoplasts for the
formation of starch-grains ; the cell-sap, therefore, becomes less
concentrated in the particular sugar entering it, and a further
osmotic diffusion into the cell takes place.
By these changes a continuous accumulation of reserve-materials
NUTRITION OF SEMI-PARASITES 225
becomes possible ; without them the cell-sap of the storage-tissues
would soon become so concentrated that a further movement of
material into the cell by osmosis could not occur. Moreover, the
change of a soluble osmotic substance into an insoluble form
prevents the turgidity of the cells from becoming excessive.
Ex. 133. Cut transverse sections of last season's branches of ash and other
trees in winter : place them for a moment in iodine solution (see Ex. 85) and
then mount in water. Examine with a low power and note in what tissues
the starch is most abundant.
5. Nutrition of semi-parasites and semi-saprophytes. Cer-
tain green plants, in addition to their power of forming organic
compounds from carbon dioxide, water, nitrates and other
simple inorganic substances, appear to derive some organic
materials ready formed either from other living plants or from
humus.
To the former class belong Yellow-rattle (Rhinanthus Crista-
galli L.), Eyebright (Euphrasia offidnalis L.), Red-rattle (Pedicu-
laris sylvatica L.), species of Melampyrum, and other semi-para-
sites not uncommon in meadows and pastures. Certain portions
of the roots of these plants attach themselves by small haustoria
(suckers) to the roots of other plants growing near them and no
doubt absorb a certain amount of organic substance from the
latter, for unless they become attached in this manner to other
plants they do not grow satisfactorily.
Many flowering plants, such as bird's-nest orchis (Neottia)
and species of Monotropa, possess few or no chloroplasts,
and live upon humus : numbers of plants, such as Heaths,
Rhododendrons, Azaleas and Winter-green (Pyrola) belonging
to the Ericaceae, Beech, Hornbeam and other representatives of
the Cupuliferae, as well as pines and Coni ferae generally, while
possessing chloroplasts appear to supplement their own manu-
factured supply of organic material by absorbing organic com-
pounds from the decaying humus or leaf-mould in which many
of their roots are found growing.
226 FORMATION OF PROTEINS
The roots of all these humus-loving saprophytes and green
semi-saprophytes possess few or no absorptive root-hairs, but
are associated with the mycelium of certain fungi present in the
humus : the associated fungus and root is termed mycorhiza. In
heaths, orchids and some other plants the mycorhiza is endophytic^
the fungus living partially within the cortex of the root, while in
beech and most Cupuliferae the fungus clings to and covers the
surface of the fine rootlets with a web-like mantle of mycelium
from which separate hair-like hyphse grow out into the humus
and absorb portions of it : the latter type is spoken of as an
epiphytic mycorhiza.
It is probable that some of the organic constituents of the
humus are dissolved by the fungus, and, with the other absorbed
constituents of the soil, are finally transmitted to the plant with
which it lives in union. The fungus thus appears to act as a
beneficial absorptive agent, and without its aid the plant does
not thrive ; beech and pine seedlings are found to grow feebly,
and die off altogether after a time, in forest soil which has
been subjected to boiling water or steam so as to kill the fungus.
As the plants of this class possessing green leaves have no
absolute need of carbohydrates from other than the usual
sources, it is possible that the fungus is concerned mainly with
the absorption and transmission of ammoniacal and organic
nitrogen compounds, as well as substances containing the ash-
constituents of the plant.
CHAPTER XVIII.
ENZYMES AND THE DIGESTION OF
RESERVE-MATERIALS.
i. THE substances stored in seeds, tubers, roots and other organs
of plants are chiefly solid, insoluble materials, such as starch and
aleuron-grains, which cannot be moved out of the closed cells in
which they occur, or are compounds such as oils and fats which,
although liquid, are unsuitable for rapid osmotic diffusion.
Before these reserve-materials can be removed from the tissues
in which they are stored to the centres of growth where they are
needed, they must be digested or transformed into soluble,
easily diffusible substances, which can travel in the ordinary
channels available for the translocation of foods. In certain
cases the necessary transformation appears to be due to the
direct action of the living protoplasm, but in many instances it
is accomplished by the chemical activity of substances termed
enzymes or unorganised ferments, which are secreted by the
protoplasm.
A considerable number of distinct enzymes are known. They
all appear to belong to the protein class of organic compounds,
and a very small amount of each is able to transform an almost
unlimited bulk of the material upon which it acts without
changing or suffering much diminution in the process. Enzymes
are inactive at low temperature, and most of them are totally
destroyed when their solutions are heated to about 70" C. : the
optimum temperature at which they carry on their work best lies
between 30 and 50* C. Their chemical activity is usually greatest
227
228 ENZYMES AND
in the dark ; exposure to bright light suspends and gradually
destroys it.
2. The following are the most important kinds of enzymes
occurring in plants :
(i) Those which transform the different insoluble carbohydrates
into sugars.
(a) To this class belong diastase which attacks starch and by
a gradual and continuous process of decomposition converts
it ultimately into maltose and a small proportion of a gum-
like substance termed dextrin. Other forms of dextrin arise
during the intermediate stages of the process but are soon
split up into maltose : some of them give a reddish -brown
colour with iodine.
Two slightly different forms of diastase are met with in plants.
The one known as diastase of secretion is concerned with the
dissolution of starch in germinating seeds, and is especially
prevalent in the germinating' grains of barley and other cereals
and grasses. This form of diastase which is the characteristic
enzyme in malt, corrodes and eats pit-like depressions in the
substance of starch-grains before finally dissolving them.
In the seeds of the Gramineae this enzyme is secreted by the
long cylindrical cells forming the surface-layer or epithelium of
that side of the scutellum of the embryo which adjoins the endo-
sperm. After its formation by the epithelium, the diastase
diffuses into the endosperm and transforms the starch into
maltose, which is ultimately absorbed by the scutellum and
transferred to the growing-points of the developing embryo.
The other form of diastase is spoken of as diastase oj
translocation. It is more widely distributed than the diastase
of secretion, being found in the leaves, shoots and other
vegetative parts of plants. The amount present in leaves is
greatest during the night or when the plant is kept in darkness.
By its agency, the starch produced in the chloroplasts of green
leaves during the daytime is transformed into sugar at night.
DIGESTION OF RESERVE-MATERIALS 229
The same form of diastase is found in all parts of sprouting
potato tubers, but is especially abundant near the ' eyes' where
growth commences. It converts the starch of the tuber into
sugar, which latter compound is subsequently transported to
the growing shoots. Small amounts are also secreted by the
' aleuron-layer ' in the endosperm of cereal grains when germina-
tion takes place. Translocation-diastase acts more readily at
lower temperatures than the diastase of secretion and dissolves
starch-grains without previously corroding them.
(b) During the germination of the cereal grains it is found that
the cell-walls of the endosperm-tissue lying near the embryo
and near the * aleuron-layer ; are disintegrated and dissolved by
the activity of an enzyme, which commences its work before the
diastatic enzyme begins to dissolve the starch in the grain.
This enzyme, named cytase, is secreted partially by the
epithelium of the scutellum, but more especially by the cells
of the * aleuron-layer/ It is also present in the cotyledons of
germinating peas and in the endosperm of buckwheat. Its
function in these cases appears to be that of getting rid of the
cell-walls, so as to allow of an easier diffusion and therefore a
more rapid action of diastase upon the starch-reserve.
Cytase is also found in the seeds of the date-palm, and is most
probably present in germinating seeds of all those plants whose
store of reserve-food for the embryo consists of thickened
cell-walls composed of hemicellulose.
(ii) The reserve-material, inulin, which is present in the tubers
of the Jerusalem artichoke, is transformed when germination
begins into levulose by the action of an enzyme named inulase.
The existence of the same enzyme has been demonstrated in
the growing bulbs of snowdrop and other liliaceous plants
which contain inulin.
(iii) A very common reserve-material of wide distribution
in the vegetable kingdom is cane-sugar. Experiments suggest
that as such it is of little or no value for the immediate
230 ENZYMES AND
nutrition of protoplasm. It is however changed by the
enzyme invertase or invertin into a mixture of dextrose and
levulose, both of which sugars possess immediate nutritive value.
In roots, such as sugar-beet and carrot, a great part of the
organic material manufactured in the leaves during the first
year of growth is sent down to the root and stored in the form
of cane-sugar. This reserve-material is utilised during the
second year for the production of new stems, flowers and
seeds, but before transmission from the root to the seats of re-
newed growth, the enzyme invertase decomposes the cane-sugar
into dextrose and levulose according to the following equation :
C,,H M U + H 2 = QH U 0, + C 6 H 12
cane-sugar \rater dextrose levulose
This form of decomposition of a compound which involves
the fixation of the elements of water is termed hydrolysis or
hydrolytic decomposition, and is characteristic of the action of
the majority of enzymes of all kinds.
Invertase has been found in leaves, in the roots of young
plants, in germinating pollen-grains, and in other portions of
plants where cane-sugar "is present
(iv) Certain substances known as glucosides occur commonly
in plant-tissues : their exact function and nutritive value to the
plant are not yet understood. However, under the influence of
acids and special enzymes, they are hydrolysed into useful
sugars and other bodies, usually aldehydes or phenols.
The sugar produced is generally dextrose (glucose), hence
the term glucoside applied to such compounds.
The best known examples are amygdalm, present in many
rosaceous plants (see p. 404), sinigrin^ abundant in mustard and
other Cruciferae (see p. 388), and salicin in the willows. Some
of the astringent compounds so widely distributed in all parts of
plants and known as tannins are also glucosides.
The decomposition of amygdalin is effected by the enzyme
DIGESTION OF RESERVE-MATERIALS 231
emulsin in the presence of water, and gives rise to benzoic alde-
hyde, prussic acid and glucose according to the following
equation :
C 20 H 2r NO n + 2H 2 O - C 7 H 6 O + HCN + 2C 6 H 12 O 6
Amygdalin Benzoic prussic glucose
aldehyde acid
The glucoside sinigrin is decomposed by the enzyme myrosin
as explained on page 389.
(v) A large amount of reserve-material in the seeds of flax,
rape or colza, castor-oil and other plants exists in the form of oil
or fat. During the germination of such seeds the oil suffers
hydrolysis through the activity of an enzyme which has been
named lipast. The products of the decomposition in those cases
which have been carefully examined appear to be free fatty acids
and glycerin ; the fate of the former substances is not clear, but
it is probable that the glycerin is transformed into some kind of
sugar which travels into the tissues of the growing embryo where
some of it is not unfrequently converted into a temporary
reserve of small starch-grains.
(vi) Another group of enzymes exists in plants by means of
which the various insoluble and indiffusible proteins are hydro-
lysed into simpler diffusible proteins, termed peptones, together
with a larger or smaller amount of amides. So far as they have
been examined they all resemble the enzyme secreted by the
pancreas of the higher animals, and are termed vegetable trypsins.
The chemical changes which proteins undergo in their migra-
tion from place to place within the tissues of plants are not the
same in all cases, but the reserve proteins of many seeds are made
available for the embryo through the action of tryptic enzymes.
When germination begins the insoluble and slowly diffusible pro-
teins in the cotyledons and endosperm are decomposed into sol-
uble peptones, and one or more amides, such as asparagine, leucine
or tryosine, all of which substances circulate readily to the various
parts of the growing embryo needing nitrogenous nutriment.
232 ENZYMES
Trypsins are also met with in the leaves, stems and developing
fruits of many plants where they facilitate the rapid translocation
of proteids in such organs.
3. The power which parasitic and saprophytic plants possess
of absorbing and utilising as food the starch, proteins and various
organic materials belonging to other plants, is dependent to a
large extent upon their power of secreting diastatic and other
enzymes.
Certain parasitic fungi penetrate into the tissues of their
victims by secreting an enzyme which is capable of dissolving
the obstructing cell-walls.
The production of alcohol from sugar by yeast is apparently
effected by an enzyme named zymase, which is present in the
yeast-cells, and some of the chemical changes brought about by
bacteria are the result of the action of enzymes secreted by
these organisms.
Ex. 134. Germinate some barley grains on damp blotting-paper ; when
the plumule just appears taste the endosperm and compare its sweetness with
that of a soaked ungerminated grain.
Compare the taste of malt with that of ordinary barley grains,
Ex. 135. Prepare some thin starch-paste and a solution of malt-diastase
as described in Ex. 86.
Take two tubes of starch -paste and into one pour some of the diastase-
solution, and into the other some of the same solution after it has been
boiled three minutes and then cooled. Test with iodine for starch in both
tubes every five minutes as indicated in Ex. 86. What has been the effect
of boiling the diastase solution ?
CHAPTER XIX.
RESPIRATION.
Ordinary Respiration in the presence of free oxygen of the
atmosphere: aerobic respiration. One of the most familiar
physiological processes carried on by living animals is that of
respiration, during which there is a constant interchange of gases
between the body of the animal and the surrounding air : the
oxygen of the air is inspired into the lungs, and from the latter
carbon dioxide gas is breathed out into the atmosphere. So
long as life exists respiration goes on continuously, and one of
the certain signs of death is the cessation of the process.
Respiration, however, is not confined to animals, but is
carried on by all ordinary plants, and is as necessary for
their existence as for the existence of animals.
The amount and rapidity of respiration is usually much greater
in animals than in plants, but the process is essentially the same
in both classes of organisms. It is well known that animals die
when the supply of fresh air is cut off, and plants soon show
signs of ill-health under similar conditions. In ordinary farm
and garden practice the parts above ground always obtain
sufficient oxygen for all their requirements, but the roots of
plants are often seriously injured through want of a suitable
supply of fresh air in the soil. The unhealthy appearance of
over-watered pot plants and of crops growing in badly-drained
ground is primarily due to an insufficient supply of oxygen to
their roots. Seeds buried too deeply do not obtain sufficient
fresh air for normal respiration and either do not germinate at
all or do sp in an unsatisfactory manner.
233
234 RESPIRATION
Each living cell of the body of a plant respires, the oxygen
necessary for the process being supplied from the air which
penetrates through the stomata and lenticels and permeates
throughout the plant in the intercellular spaces.
In all the higher plants the products of respiration under
normal conditions are carbon dioxide gas and water. As the
carbon of the carbon dioxide is derived from the compounds
within the body of the plant, it is clear that the process is a
destructive one and must result in a decrease in the dry weight
of the plant The seedlings of cereals and many other plants
when allowed to grow in the dark often lose about half their dry
substance in two or three weeks.
In this respect respiration is essentially the opposite of the
* assimilation ' process in which there is a fixation of carbon and
a consequent increase in dry weight of the plant. Moreover,
respiration goes on in all living cells, both in darkness and in
light, whereas * carbon-fixation ' is only carried on by those cells
which contain chloroplasts, and in these only when they are
exposed to light.
During respiration oxygen is consumed and carbon dioxide is
set free into the air, but in green plants exposed to daylight the
' carbon-fixation ' process consumes twenty or thirty times as
much carbon dioxide as is produced by respiration during the
same time, so that when both processes are going on there is always
a decrease in the carbon dioxide and an increase in the oxygen
of the atmosphere, and only at night or in the dark does the
process of respiration become apparent. However, in parts
of plants which are not green, such as the roots, flowers
and germinating seeds, respiration is readily detectable at all
times.
The carbon compounds which disappear while respiration is
going on, are carbohydrates, such as starch and the various
sugars and fats. The oxidation of these substances does not
take place at ordinary temperature outside the plant, and the
RESPIRATION 235
manner in which they are utilised within the tissues of plants
during the respiration process is not understood. The oxidation
is controlled and 'is dependent upon the protoplasm, for respira-
tion ceases when life becomes extinct, and the amount and nature
of the chemical changes carried on are not altered either by con-
siderably reducing or increasing the amount of oxygen in the
surrounding atmosphere.
The absorption of oxygen and the subsequent emission of
carbon dioxide are the beginning and end respectively of a
long series of chemical changes, the intermediate stages of which
are at present unknown.
The disappearance of starch, sugars, fats and other carbon
compounds during respiration is not due to simple direct oxida-
tion ; probably the protoplasm itself is directly attacked by the
absorbed oxygen after which it uses up the carbon compounds
to repair its waste.
The proportion of oxygen absorbed to the carbon dioxide gas
given off is dependent on the energy of growth and on the
materials consumed during respiration. In certain plants the
volume of carbon dioxide produced , , P , . .
ratl ^volume of oxygen Juried- haS been f Und tO be aS loW
as *3, while in others it has been observed as high as 1*2.
In germinating seeds, tubers and bulbs containing starch and
sugars, and in most flowering plants, the volume of oxygen
taken from the air during active normal respiration, is equal to
that of the carbon dioxide exhaled ; but in the respiration carried
on during the germination of seeds containing fats and oils, the
volume of oxygen consumed is greater than that of the carbon
dioxide exhaled, some of the oxygen absorbed by such seeds
being apparently used up in oxidising the fats into some form
of carbohydrate.
It is by means of the energy set free by the oxidation of
various compounds in the respiration-process that the plant is
enabled to maintain its vital activity, and the vital energy of
236 RESPIRATION
animals originates in a similar manner : when the physiological
oxidation is prevented growth ceases, the streaming movement
of the protoplasm within the cells is stopped, and the move-
ments of the leaves, roots, stems and other organs of plants are
suspended.
In all cases heat is produced during respiration, and in warm-
blooded animals it is easily perceived. In plants, oxidation is
generally much less energetic than in animals, and the heat
produced is so slight that no difference in temperature can be
detected between green plants and that of the air surrounding
them. Moreover, in ordinary green plants exposed to the air,
the cooling effect of transpiration masks any slight rise in tem-
perature due to respiration. However, when actively germinat-
ing seeds or rapidly expanding flowers and buds are heaped
together, a rise of two or three degrees above that of the
atmosphere may be readily observed, by placing the bulb of
a thermometer among them.
The amount of respiration is dependent on external and
internal conditions, and in different parts of the same plant
the activity of the process is not the same. In all young actively
growing parts rich in protoplasm, such as germinating seeds,
expanding buds and flowers, respiration is vigorously carried on,
and the same is noticeable in injured cut portions of plants.
In dormant bulbs, tubers and buds little or no respiration is
observable. In dry seeds respiration seems to be entirely
suspended, and many have been kept for twelve months in a
vacuum, and in nitrogen and other gases under conditions which
render respiration impossible, yet after such treatment the seeds
germinated freely.
At freezing-point and a degree or two below it, where growth
is stopped, respiration may frequently be detected. With in-
creasing temperature there is a steady increase in the amount of
respiration up to the point where death takes place, and the
process stops suddenly.
RESPIRATION
237
Light appears to have no direct influence upon it, respiration
continuing very similarly both in darkness and light.
It has also been found by experiment that the process goes
on quite normally even when the proportion of oxygen in the
surrounding atmosphere is reduced to less than half that
ordinarily present in the air.
Ex. 136. Soak a handful or two of peas or barley grains in water for
twelve hours. Take them out of the water and allow them to germinate on
damp blotting-paper for twelve hours. Then put them in a wide-necked
bottle, cork the latter and place it in a warm, dark room. Cork and place beside
it another similar but empty bottle. Allow both to remain for twelve hours,
after which time test for the presence of carbon dioxide by introducing a
lighted match or taper into the bottles : the light is extinguished by carbon
dioxide. Arrange another similar experiment, and test for carbon dioxide
with lime-water : pour in the lime-water, and shake the bottles ; the lime-
water becomes milky if carbon dioxide is present.
Ex t 137. Partially fill a wide-necked bottle with half expanded young
dandelion or daisy * heads' ; cork and leave for twelve hours, after which
time test for carbon dioxide as above.
Ex. 138. Repeat the experiment above, using green leafy shoots, expand-
ing buds, bulbs, tubers and other portions of plants.
Ex. 139. Soak some peas for twelve hours,
and after taking them out of the water allow
them to germinate on damp blotting-paper for
a few hours. Then place them in a flask ar-
ranged on a retort stand, with a tightly fitting
rubber stopper and bent glass tube as in Fig.
89. Slightly warm the flask with the hands
and dip the open end of the tube (a) into
mercury in a beaker (/?). Leave the apparatus
for ten or twenty minutes and fasten a piece
of gummed paper on the tube (a) at a point
(x) up to which the mercury rises in it. Keep
the whole in a room of even temperature for
D ten or twelve hours, and observe the position
-of the mercury at the end of that time. If
the volume of oxygen absorbed is equal to that
of the carbon dioxide emitted, the mercury will remain at the same place in
the tube.
Repeat the experiment with oily seeds, such as hemp, linseed and turnip.
FIG.
2 3 8
RESPIRATION
With these the mercury rises in the tube, for the volume of oxygen absorbed
by them is greater than that of the carbon dioxide emitted.
Ex. 140. Show that heat is developed during respiration of germinating
seeds.
Soak some barley grains or peas
in water for a few hours and then
allow them to begin germinating on
damp blotting-paper. Place them in a
large glass funnel (/>'), suppoitcd in a
beaker or glass cylinder (6") containing
a small quantity of a strong solution of
potash (D] ab in Fig. 90 ; dip into
the seeds the bulb of a thermometer (A]
reading to half a degree. Cover the
whole loosely with a cardboard or
wooden box [E], leaving a hole in the
top for the thermometer tube.
For comparison, fit up a similar
apparatus by the side of the first with
balls of blotting-paper soaked in water 7 *
in the funnel instead of seeds ; compare
<lG '
the readings of the t\\o thermometers on three succeeding days.
Anaerobic or Intramolecular respiration. When living plants
or parts of plants are placed in an atmosphere devoid of free
oxygen, they continue to give off carbon dioxide gas for a longer or
shorter time before death occurs. This production and evolution
of carbon dioxide by living organisms in the absence of free
oxygen is termed anaerobic or intramolecular respiration,
The length of time which plants will live under these circum-
stances depends upon the kind of plant and the vigour of its
growth : actively-growing maize seedlings live and continue to
give off carbon dioxide in the absence of oxygen, for twelve
or fourteen hours at ordinary temperatures, while ripe fruits,
such as pears and apples, live for several months under similar
conditions.
In the majority of cases the amount of carbon dioxide thus
produced is considerably smaller than that which is given off
by the same plants when exposed to the air ; for a short time,
RESPIRATION 239
however, bean seedlings and other plants emit the same or
a greater volume of carbon dioxide when placed in an atmo-
sphere free from oxygen, as they do when growing normally in
the air.
During intramolecular respiration carbohydrates and fats
disappear from the tissues of the plants just as in ordinary
respiration in the presence of abundance of oxygen, but the
production of carbon dioxide is accompanied by the formation
of alcohol and other compounds. The alcohol produced during
the intramolecular respiration of ripe cherries amounted in
one of BrefekTs experiments, to more than two per cent., and
in pea seedlings to over five per cent, of their fresh weight.
While the higher plants are unable to maintain their vitality
in the absence of free oxygen for more than a short time,
many of the lower forms of plant life, such as yeasts and
bacteria, are independent of the presence of free oxygen and
continue to live and multiply without it (p. 785).
CHAPTER XX.
GROWTH.
i. Growth. We have seen in a previous chapter that at the
apex of a stem or root of an ordinary green plant, there is usually
a formative region where the component small cells are in a state
of division, and new cells are being manufactured. Immedi-
ately behind this is a longer or shorter portion which may be
designated the growing region of the stem or root. Here the
cells are found to be turgid, and in consequence of the pressure
within them have increased in size, and at the same time many
of them have become changed in form.
These changes of size and form, owing to increased turgidity
do not, however, necessarily constitute growth, although they
are always associated with growth. Cells which are growing not
only become distended by the osmotic pressure within the
vacuoles, but also undergo a permanent change in size, form
and structure, in consequence of the deposition of substances
in their cell-walls and other parts; on withdrawing water from
such cells the original state in which they existed when first
produced in the formative region is not again reproduced by
such a proceeding. Moreover, since the growth of a cell cannot
go on without increased turgidity, and as this involves an
addition of water to the vacuole of the cell, there is always an
increase in the total weight of the cell when growth is proceed-
ing : however, on account of the loss of substance by respiration,
there may be a decrease in its dry weight if such loss is not
compensated by anabolic nutritive processes.
What is true of a single growing cell is also true in the case
240
GROWTH 241
of the whole growing region of a shoot or root, for the latter
is merely composed of a number of active cells.
Although it is not possible to define in a single sentence the
exact meaning or connotation of the term growth, it may
generally be taken to imply a permanent change in the form
of a living organism or some of its members, and that the region
which is growing is also increasing in weight.
The actual growing regions of the shoots developed in the
dark from a potato tuber not only change their form but also,
while they are growing, increase in weight at the expense of
the water and reserve-food drawn from the tuber. It will be
found, however, that the total weight of the tuber (which does
not grow) and its growing shoots decreases in consequence of
the loss of water by transpiration and by loss of carbon dioxide
in the respiration process.
During the early stages of its life when a plant emerges from
the seed, growth takes place in all parts of its body. After a
time, however, growth is confined to certain special localised
portions, or growing points , and to the cylindrical cambium-
tissue which brings about secondary growth in thickness of
dicotyledonous stems.
The growing-points in the case of stems and roots are generally
terminal, or situated near the ends of these members : in such
cases the youngest part is nearest, and the oldest part farthest
away from the apex of the shoot or root.
In the stems of grasses their increase in length is due to the
activity of growing-points which are situated at the base of the
internodes ; moreover the growth in length of the long leaves of
onions and rushes, and that of many peduncles of flowers goes on
at the base of the structures, their tips being the oldest parts :
growing-points of this character are described as intercalary.
When a cell or a plant member begins to grow its rate of
growth is at first slow ; afterwards it grows more and more
rapidly until a maximum rate is attained, after which the growth
24* GROWTH
diminishes gradually until it ceases altogether when the part is
mature. The time occupied by this gradual rise and fall is
termed the grand period of growth.
It is also noticed that the vigour or energy of growth of a stem
or other member varies during the grand period : at one stage
of the development of the complete stem the growing part either
grows more rapidly or continues its growth longer than at
another stage. For example, during the youngest stages of the
development of most stems the energy of growth is low and
short internodes are produced, later the energy increases, and
larger internodes arise, afterwards the length of the internodes
diminishes in consequence of a gradually decreasing energy
of growth.
Ex. 141. In autumn before the leaves have fallen, cut off branches from
the common trees and shrubs, and measure the length between the several
internodes on that part of each branch which has grown during the same
season.
Note the general rise and fall in the length of the internodes.
Note also the relative size of the leaves at each node.
Make similar measurements on the stems of annual herbaceous plants.
Ex. 142. Repeat experiments 15 and 20: similarly mark with Indian
ink at intervals of & inch the second and third leaves of a young onion plant
soon after they appear ; measure the intervals after the leaves have con-
siderably lengthened, and compare the growth with that of a bean root.
Is the region of greatest growth near the end of the leaf?
Ex. 143. Select a stem of wheat or barley in which the ear is just ap-
pearing ; cut about half-an-inch below the first and also below the second
visible node from the top, so as to obtain about one internode of the stem.
Remove the leaf-blade and a small portion of the leaf-sheath and care-
fully measure the total length of the stem and the small part of it below
the node. Make five or six marks with Indian ink J of an inch apart at
the upper part of the stem. Then place the lower end of the stem in
water, cover the whole if possible with a glass globe and leave it in a warm
room for twenty-four hours; or place the stem in a glass cylinder with a
little water at the bottom for a similar period.
Measure again the total length ; how much has the stem grown, and has
the growth taken place near its upper marked end or near the base ? Has
the small portion below the node grown at all ?
Ex. 144. Measure the length of the internodes on a few shoots of any
CONDITIONS WHICH INFLUENCE GROWTH 243
rigorous common trees, shrubs or herbaceous plants in early summer when
they are beginning to grow, and at intervals of two or three days for some
time afterwards.
Determine the time during which an internode continues to grow in length.
2. Conditions which influence growth. Only living plants
grow and the cells of the growing parts must be in a youthful
state. Various external conditions are also necessary for healthy
growth, the chief of which are : (i) a suitable temperature ;
(ii) an adequate supply of water ; (iii) appropriate food or food-
materials ; (iv) the presence of oxygen, (v) Light although not
absolutely essential to growth has a beneficial influence upon it.
(i) Heat. It is well known that growth in winter, when the
temperature of the surrounding aii and soil is low, goes on
very slowly or not at all. As the temperature rises in spring
seeds readily germinate and the buds of plants commence to
grow ; with the increasing warmth of summer growth becomes
more and more energetic.
By subjecting a plant to a gradually decreasing temperature, a
point is at last reached at which growth entirely ceases ; this
is described as the minimum temperature for growth. It is
not the same for all plants ; the seeds of many common weeds,
and mustard and cress germinate, and the fully developed
plants continue to grow near freezing-point, while those of the
cereals are stopped when the temperature falls to about 5 C.
On the other hand the seeds and plants of maize and the
scarlet-runner bean cease to grow at about 10* C., while the
minimum temperature for the germination and growth of the
cucumber, melon, and many tropical plants is as high as 19
or 20* C.
By raising the temperature from the minimum, a point is
reached at which growth goes on most rapidly ; this is termed
the optimum temperature. By further increasing the temperature
beyond the latter point, growth becomes slower and slower
until a maximum is attained, at which growth is entirely checked
244 GROWTH
Thus it is seen that plants may be too hot or too cold for
growth, and between these extremes there is an optimum or
best temperature where they make the most satisfactory
progress.
The optimum temperature for most common farm and garden
plants is about 28* C., while the maximum usually lies between
38 and 43* C. ; the optimum for maize, scarlet-runner, bean and
cucumber is about 33 or 34 C., the maximum about 46 C.
It may be conveniently noticed here that although ordinary
plants in an active state of growth have their development
stopped at the temperatures indicated above, the death of the
protoplasm does not usually take place until the higher tempera-
ture of about 56 C. is attained or until it has been cooled to
freezing-point or several degrees below the latter.
The power of withstanding heat and cold depends very largely
upon the amount of water which the plant contains.
Well-ripened shoots and buds containing little water do not
suffer so much from the effects of frost during winter as sappy
immature shoots which contain a larger proportion of water.
Turgid seedlings, buds just opening and recently unfolded
leaves, plants watered in the evening, succulent roots and all
parts containing considerable amounts of water are often injured
by exposure to sharp frost for a few nights.
Usually when a plant is subjected to a temperature of 2* to 5* C.
the cytoplasm allows a certain amount of pure wat^r in the vacuole
to ooze out of the cell into the surrounding intercellular spaces
where it freezes into small crystals of ice : death in such cases
is somewhat analogous to death by drying. Although plants are
sometimes killed in the process of freezing, this formation of ice
is not always fatal, for in many cases, if the frozen part is thawed
very slowly, the cells re-absorb the water and the tissues assume
their normal state. If, however, the frozen part is thawed rapidly
the water does not re-enter the cells and death takes place.
Frozen potted plants should not be exposed to the direct rays
CONDITIONS WHICH INFLUENCE GROWTH 245
of the sun ; syringing with ice-cold water is often a useful method
of thawing them.
In long-continued frost the water frozen on the outside of the
cells may gradually evaporate into the dry cold air ; under such
circumstances the frozen parts shrivel and die of thirst.
Dormant seeds contain little water and are able to withstand
the lowest temperature attainable without injury ; recently Dewar
and Dyer found that the seeds of mustard, wheat, barley, pea
and other plants germinated freely after being soaked for six
hours in liquid hydrogen, the temperature of which was 453* F.
below freezing-point.
In actively growing plants the protoplasm becomes disorganised
and its vital powers destroyed at temperatures about 45 or 50 C
Many dry seeds withstand a dry heat of 80 C. or higher for
an hour or longer; after soaking, however, they are killed by
10 to 30 minutes' exposure to a temperature of 51 or 52 C.
(ii) Water. Water is necessary for the maintenance of the
turgidity of the growing cells. It is itself a food-material and is
also essential as a vehicle for the transport of foods and food-
materials needed for the nutrition of the growing organs.
When plants from the beginning of their lives suffer from want
of water their size is much diminished, although in other respects
their development appears normal; individually they become
dwarfs.
On persistently dry soils and in dry seasons the bulk of the
hay crop, the size of the 'roots' of turnips, the height of the
straw of cereals, and the size of the various members of plants
are proportionately decreased, while in damp seasons or upon
soils which hold considerable amounts of water, the growth of
plants is much increased. The growth and consequent size of
plants in pots is similarly increased or decreased by judiciously
varying the water-supply during the time that growth is pro-
ceeding.
Somewhat sudden diminution in the supply of water results in
246 GROWTH
the rapid cessation of growth followed by withering of the whole
plant.
(iii) Food is essential for the construction of the protoplasm
and cell-walls of the growing parts.
(iv) Oxygen is necessary for the process of respiration without
which all vital functions cease.
(v) Light. The various members of a plant's body grow more
rapidly in feeble light than when they are strongly illuminated :
that is, light retards growth.
When grown in darkness for a considerable time plants
become peculiarly modified, in which condition they are said to
be etiolated.
Among dicotyledons the internodes of the stems of etiolated
specimens are abnormally elongated and much more slender
than similar parts grown under ordinary conditions of day
and night. Their cells are larger than usual and the cell- walls
remain thin; the stems in consequence become weak and
are unable to maintain a normal erect position. The whole
plant contains more water proportionately to its size and the cell-
sap is usually more acid than that of normally grown plants.
The leaves of etiolated dicotyledons do not develop but
remain small and scale-like and as the chlorophyll does not
develop in the plastids the whole plant appears pale in colour.
A few stems such as those of iris and onion, and the
hypocotyls of many plants, such as the bean, which ordinarily
grow in the dark, do not exhibit the peculiar phenomena
of etiolation, nor are the leaves of iris and other similar
rhizomatous and bulbous monocotyledons dwarfed when grown
in darkness.
The development of the flowers of plants goes on in darkness
much the same as in the light.
Ex. 145. Sow two sets of peas, beans, mustard, and barley in pots,
and allow them to germinate. When the young plants just appear on the
surface of the soil, place one set of each in a light situation but not in the
SPONTANEOUS MOVEMENTS OF GROWTH 247
direct rays of the sun, and the other set near them but covered with boxes
which exclude all light.
(i) From time to time measure and compare the diameters of the stems and
the lengths of the internodes of the plants growing in the light with those of
the plants growing in the dark.
(ii) Measure and compare the length and breadth of the leaves of the two
sets of plants.
(iii) Note the differences in the colour and firmness of the two sets of plants.
Ex. 146. Make observations similar to the above on the shoots developed
in light and in darkness respectively, from the tubers of the potato and
artichoke, those springing from the roots of the dahlia, and the leaves
of onions.
3. Spontaneous movements of growth : nutation and tissue-
tension. Growth rarely proceeds evenly in all parts of a shoot,
root, or other organ of a plant ; certain portions grow more
rapidly or continue to grow for a longer period than adjoining
parts. In consequence of this uneven growth the organs of
plants (i) exhibit peculiar, slow, spontaneous movements, and
(2) their tissues become subjected to pressures and tensions in
various directions.
In stems and roots the growth of one side is more rapid than
the other : the more rapidly growing side becomes slightly longer
than the other, and the whole growing part forming the end of
the stem or root becomes bent or curved in consequence.
The side on which most rapid growth occurs is not always
the same but varies from hour to hour, so that the growing
organ bends over in different directions and the tip travels
slowly round and round, following a spiral line in its upward
or downward growth. Movements of this kind are spontaneous
and automatic : like the rise and fall in the rate of growth
during the grand period they originate within the growing
organ itself and occur whether the plant is kept in darkness or
exposed to the light.
To such slow nodding movements the term nutation is
applied.
In most stems and roots their tips travel round from right
248 GROWTH
to left or in a direction the opposite to that of the hands
of a clock ; but the apex of the stem of a hop, honeysuckle
and some other plants moves round from left to right when
nutating.
By means of such movements roots are enabled to make
easier progress through the soil, and climbing stems and ten-
drils which nutate very conspicuously are enabled by the same
means to reach neighbouring supports around which they wind.
The ends of the subterranean shoots of many dicotyledonous
plants are bent round by the excessive growth of one side
in the manner indicated in Fig. 4. By such arrangement
the delicate tissues of the terminal buds are considerably
protected against injury when the shoot is growing forward
or upward through the soil. After such a bent shoot emerges
from the soil, rapid growth takes place on its concave side and
the curved portion soon becomes straight.
In a young state the leaves forming the buds of plants are
curved round the delicate growing-point or curled up in a
characteristic manner in consequence of the growth of one side
of each leaf proceeding faster than that of the other side : when
the buds open the side which previously grew more slowly grows
at a greater pace and the curled leaf consequently unfolds and
eventually becomes flat.
In most stems the pith and cortex continue to grow for a
longer period than the woody tissue : the pith and cortex strive
to elongate but the woody tissue hinders them to a certain
extent. The result of such unequal growth is the production
of longitudinal tensions in the growing parts. On splitting in
two the stems of elder, sunflower and other rapidly growing
plants longitudinally the pith elongates a little and the two
separated halves curve outwards.
The bark of many trees does not grow so rapidly as the wood
within, and consequently becomes more or less stretched.
It must be mentioned that movements of plant organs and
SPONTANEOUS MOVEMENTS OF GROWTH 249
tensions in their tissues may be set up by inequalities in the
turgidity of the various component cells as well as by irregular
growth : both causes play a part in many instances of plant
movements.
Er. 147. (i) On a warm day when there is no wind examine some young
plants of scarlet-runner beans, hops and other twining plants which are
growing round upright poles or string. Draw a line on the ground from the
base of the pole, in the direction in which the tip of the stem is found at the
time. Examine the plants at intervals of half an hour and similarly mark
the direction in which the tip is curved over at these times ; try and deter-
mine how long it takes the tip to make a complete revolution round the pole
as a centre.
(ii) Make similar observations on the nutation of the tip of the stems of
runner bean plants grown in large pots and allowed to wind round sticks
stuck in the soil. The plants should be placed out of doors, not in direct
sunlight.
Ex. 148. Place some soaked broad beans with the micropyle downwards
in damp sawdust, and allow them to germinate. When their roots are about
an inch long take them up and select one with the straightest root. Pin it
through the narrowest diameter of the cotyledons to a slender stick or thin
piece of wood and place the latter through a hole in a sheet of cork or card-
board. Then place the cardboard with the bean attached over the neck of a
wide-mouthed bottle containing a very little water, and arrange that the root
is vertical within the bottle.
Stand the whole in a dark cupboard or cover it with a box to exclude the
light.
Examine the root after 12, 24, 36 and 48 hours and see if it remains
vertical or if it nutates in any way.
Does it nutate more in the plane of the cotyledons than at right angles to
this plane ?
Ex. 149. Cut pieces two inches long from ihe full-grown stems of a sun.
flower and other plants. Carefully measure and then split them into longi-
tudinal strips, so as to include in some the pith only and in others the cortical
tissues only. Measure the separate strips and compare their lengths with
each other and with the original length of the whole piece.
Note also the form of the separate pieces.
Ex. 150. In July or August and at other times remove a complete ring of
bark an inch long from three or four-year-old branches of sycamore, birch,
beech and willow. Then try and place the bark in its original position on
the shoot : does it fit exactly ?
250 GROWTH
4. Induced movements of growth. In addition to the vital
movements previously discussed which arise in consequence
of internal inherited causes operating within the plant organs
themselves, other movements are observable in various organs
of plants, which are induced by some external provocation or
stimulus.
The protoplasm of living plants is irritable and sensitive like
that of animals only in a somewhat different manner, and is
capable of responding to the action of various external influences.
The chief exciting causes which induce movements in the
different plant members are (i) contact with a foreign body ; (ii)
alterations in temperature and the periodic alternation of day
and night ; (iii) lateral or one-sided illumination ; (iv) the force
of gravitation ; and (v) variations in moistness of the surrounding
soil and atmosphere.
(i) Movements induced by contact with a foreign body,
The best examples of movements of this class are met with in
tendrils and roots of plants.
The tendrils of peas, vetches, vines, passion-flowers and other
plants are susceptible to slight contact.
If a tendril while nutating round and round touches a foreign
body, such as the stem or twig of a neighbouring plant, it begins
to curve towards the irritating structure. If the latter is not too
thick and contact with it is prolonged the tendril becomes more
turgid on the side not irritated and also grows more rapidly on
the same side, so that the tendrils soon coil completely round
the structure.
The particular part of the tendril which is sensitive varies in
different plants : sometimes a considerable portion all round the
tip is irritable, while in other cases the sensitive region is limited
to a short part on one side only. The curvature of the tendril
is not confined to the portion actually irritated, but the stimulus
is usually transmitted backwards along the tendril, and coiling
takes place in the parts which have not been touched.
VARIATIONS IN TEMPERATURE 251
Similar response to contact with a neighbouring foreign body
is met with in the sensitive petioles of certain climbing species
of Tropaolum and Solanum, and in a lesser degree is observable
in many twining and climbing stems.
Small portions near the tips of roots are sensitive to prolonged
lateral contact : when such parts touch stones and other hard
objects in boring their way through the soil, they curve away
from the irritating bodies and the root tips continue their
growth in a new direction.
On the other hand the older portions of growing roots when
stimulated by contact curve towards and endeavour to grow
round the irritating objects.
Both these and the nutating movements previously mentioned
are such as enable roots to pass obstructing objects in their path.
Ex. 151. (i) Observe the form of the free tendrils of the vetch, pea, vine
and white bryony (Bryonia dioica L.). Compare with tendrils attached to
their supports.
(ii) Arrange so that some of the free tendrils which are about three parts
grown shall come in contact near their tips with small twigs or other similar
support. Examine at intervals of a few hours and note the amount of
twining of the tendril round its support.
(iii) Stimulate the concave side of the curved end of a tendril of white
bryony, cucumber or melon for about a minute by rubbing with a moderately
smooth piece of wood, and then watch its subsequent behaviour for two or
three minutes. Does its curvature increase ?
Ex. 152. Examine the mode of climbing of Solatium jasminioides.
(ii) Movements in response to variations in temperature, and
the changes of day and night. Tulips, crocuses and other
flowers open on a warm day or when brought into a warm room
and close when placed in a cool situation. The opening and
closing movements go on independently of light and are brought
about by alterations in the growth and turgidity of the cells
forming the upper and lower sides of the petals ; the change of
temperature stimulates the protoplasm in such a manner that
varying amounts of water are allowed to pass through it into
252 GROWTH
and out of the vacuoles of the cells, and the turgid condition of
the cells becomes altered in consequence.
The flowers of scarlet pimpernel and other plants close in the
daytime if the weather is dull and the air damp. By closing
during unfavourable weather the stamens and other reproductive
parts are protected against possible injury from rain and other
causes, and by opening on warm days the plant secures a better
chance of cross-pollination, for only at such times are insect
visitors abundant.
The leaflets of the compound leaves of the clovers, medicks
and other Leguminosae, as well as those of wood-sorrel and other
plants, fold together or change their position in a characteristic
manner at night and open out again next morning. Movements
of this kind are termed nyctitropie or sleep-movements^ and are
effected by the plants in response to the stimulus of varying
temperature and altered illumination occurring during the
changes from day to night. Frequently the edges of the leaves
and leaflets are turned upwards at night, or the whole leaf
droops or is folded in such a way that the leaf-area presented
to the sky is much diminished, and loss of heat by radiation is
consequently reduced. By taking up such positions at night
the leaves are considerably protected from being injured by cold
Ex. 153. Examine the ' day' and 'night positions ' of the leaves of clover,
medicks and runner beans.
In the daytime cover up a white clover plant with a bowl or basin, and
after two hours compare the induced ' night position ' of the leaflets of the
darkened plant with the day position of the leaflets on a neighbouring ex-
posed plant.
Ex. 154. Compare the day and night positions of the flowers of wild
carrot, Herb Robert (Geranium Robertianum}> and wild pansy.
Pluck two or three full-grown crocus and tulip flowers when closed in the
morning of a dull day ; place their stalks in water and convey them to a
warm room. Notice how soon they open : after opening, stand them in a
cool place and observe how soon they close.
Ex. 155. On a bright day pluck some well-opened heads of daisies and
dandelions : place the stalks in water and then transfer them to a dark
LATERAL ILLUMINATION I HELIOTROPISM 253
cupboard. Note that the heads close after being kept an hour or two in
darkness. Remove them to a bright situation and observe if they open
again.
(iii) Movements induced by lateral illumination: heliotropism.
When a plant is allowed to grow undisturbed in the window
of an ordinary room, one side of its stem is illuminated much
more than the other ; in consequence of such lateral illumination
the growing part slowly bends over towards the light so that the
tip and a certain amount of the stem behind it ultimately points
in the direction from which the light comes. Similar curvature
is seen in stems of plants growing near walls, and in other situa-
tions where they receive light on one side more than the other.
This bending like other cases of the curvature of growing
members is due to a difference in the rate and amount of
growth on the two sides of the stems, and like the movements of
leaves and roots mentioned below, is effected in response to the
stimulus of light falling upon the stem from one side. A small
portion near the tip of the stem is specially sensitive to lateral
illumination, and the stimulus it receives appears to be conducted
back to the part which bends in the peculiar manner described.
If the tip of the stem of a seedling which exhibits such move-
ments is cut off or carefully covered by a cap of some material
through which light cannot pass, the characteristic curvature
does not occur.
The same stimulus of lateral light when applied to roots
induces an opposite movement from that observable in the
growing part of a stem. The growing part of a root curves
away from the stimulating light, and the tip and a small portion
near it, although they lie in the line of the incident light, point
away from it.
The movements in response to the stimulus of lateral light
in which the plant members turn towards the light, like stems,
are spoken of as heliotropism or positive heliotropism^ while the
term apheliotropism or negative heliotropism is applied to move-
254 GROWTH
ments in which the organ stimulated curves away from the light,
like roots.
The utility of these movements is clear : by such movements
stems are enabled to reach the light and so place the leaves
which they bear in the most favourable position for carrying on
their function of * carbon-fixation/ and roots are aided in finding
their way and penetrating into the dark crevices of the soil.
The leaves of an onion and the flat sword-like leaves of
certain monocotyledons appear to be heliotropic like stems, but
the majority of the ordinary green leaves of plants behave
differently from either roots or stems. They usually turn or
twist on their petioles so as to place the upper surfaces of
their blades at right angles to the direction in which the light
falls upon them; plant members taking up such a position in
reference to the incident light are described as diaheliotropic.
A few stems, such as those of the ivy, appear to be dia-
heliotropic. Instead of bending away from a wall they grow
close up to it, and need no special training to keep them there.
The ordinary heliotropic stems of fruit-trees, however, growing
in a similar situation curve away from the wall, and if this is
to be prevented the growing tips must be secured until they
have become mature and firm.
Experiments have proved that only the blue and violet rays
of light are effective in inducing heliotropic movements : no
response is made to red and yellow rays.
Ex. 156. Sow some mustard seeds in two small three-inch flower-pots,
and when the plants are about an inch high place one pot of the seedlings
in a box in total darkness, the other pot cover with a box blackened in the
inside with lamp black, and having a hole bored in one side about on a
level with the top of the seedlings.
Allow the seedlings to grow, and in a day or two compare the direction
of growth of their stems in the two pots.
Ex. 157. Germinate a few mustard seeds in damp sawdust, and when
their primary roots are about an inch or an inch and a half long take one
or two of the seedlings and push their roots through holes in a strip o/
FORCE OF GRAVITATION I GEOTROPISM 255
cardboard. Afterwards plug the holes gently with cotton wool so as to
prevent the seedlings from slipping, and then place the cardboard over a
beaker of well water so that the roots of the plant may dip vertically into
the water.
Place the whole in the darkened box with a hole in the side as described
above, and allow the seedlings to grow : examine in a day or two and note
if the root and stem are vertical as arranged when first put into the box.
Ex. 158. Examine fuchsias, geraniums and other plants growing in
windows, and note the bending of the stems towards the light.
Note that the leaves have their upper surfaces towards the light.
Observe the leaves of ivy shoots and other plants growing close to a wall ;
their upper surfaces are towards the light. Do the leaves grow out all on one
side of such stems ? Have the petioles curved in any way ?
(iv) Movements in response to the force of gravitation:
geotropism. All bodies on the earth behave as if they were
attracted towards the centre of the earth by a force which is
spoken of as the force of gravitation. This force exerts a
peculiar stimulating influence upon the various members of
living plants. Most primary stems grow vertically upwards
against the force and away from the earth ; when displaced
into a horizontal position, the growing regions near the ends
of the stems slowly bend upwards until they are again vertical.
Primary roots, on the other hand, grow downwards with the
force and towards the centre of the earth : when the primary
roots of seedlings which have been allowed to grow straight
down are placed horizontally, their growing parts soon curve
through a right angle and take up a vertical position with
the tips pointing downwards.
Roots are described as geotropic or positively geotropic^ while
stems which grow away from the earth are spoken of as apogeo-
tropic or negatively geotropic.
The rhizomes of couch-grass, potatoes, and other plants are
generally diageotropic ; they grow in a horizontal position and
when placed vertically begin to slowly curve to one side until
the growing regions and tips are parallel with the surface of
the ground.
18
256 GROWTH
These movements go on in the dark, and are the result of
stimulus of gravity acting upon the sensitive tips of the stems
and roots and not directly upon the growing parts which become
curved.
The lateral secondary branches of roots and stems appear
to be less sensitive to the action of gravity than primary
members ; for example, secondary roots grow obliquely and
not vertically downwards in the soil.
The peduncles of most flowers are generally apogeotropic but
in some cases their geotropic irritability changes when the flower
opens : many varieties of daffodil become diageotropic when the
flower opens, the * trumpet ' of the corolla then taking up a more
or less horizontal position.
The stems of wheat, barley and grasses generally curve up-
wards at the nodes when they are bent on one side by the wind
and rain, and the upper internodes and ears may eventually
attain an erect position after the crop has become * laid/ if the
latter does not happen too late in the season.
This apogeotropic movement of a cereal stem is due to the
stimulus of gravity which induces a renewal of growth in the
tissue forming the swollen leaf-bases close to the nodes.
Ex. 159. Repeat Ex. 9, and note the geotropic behaviour of the roots
and stems of the beans employed.
Ex. 160. Sow a runner bean in a pot of garden soil and keep in a dark
place. When the stem of the seedling is two or three inches long turn the
pot on its side so that the young stem is horizontal and leave it to grow in
the dark as before. After a few hours examine and note the curvature of
the stem : which part has curved most ?
Ex. 161. Cut a straight piece of a young barley or wheat stem with a
node about the middle of it, and place the lower cut end through a hole in a
cork which fits into a small flat medicine bottle. Fill the bottle with water,
insert the cork with the straw through it, and place the bottle on its side so
that the straw is horizontal. Leave it in a dark cupboard all night and
examine next morning. Is the straw still horizontal ?
(v) Movements induced by variations in moistness of the
MOISTNESS OF THE SOIL : HYDROTROPISM 257
soil: hydrotropism. The tips of roots are sensitive to changes
in the moisture of the soil : while growing through the ground
they bend towards the parts which are dampest. In consequence
of this peculiarity, the roots of plants frequently find their way
into drain pipes, wells and water courses some considerable
distance away from the place where the stems are growing.
CHAPTER XXI.
REPRODUCTION.
i. THE physiological processes previously discussed have been
concerned with the maintenance of the life of the individual
plant. It is now necessary to consider the process of reproduc-
tion^ or the power of giving rise to new and separate individuals,
which is one of the most characteristic peculiarities possessed by
all living organisms.
Among flowering plants two distinct modes of reproduction
are met with, namely, (i) vegetative reproduction and (ii) sexual
reproduction.
VEGETATIVE REPRODUCTION.
2. The essential feature of vegetative reproduction consists
in the separation either naturally or artificially of portions of the
vegetative organs of the parent, each detached part subsequently
developing into a new and complete individual plant. A good
instance of natural vegetative multiplication is seen in the potato.
Thin underground rhizomes grow out from the parent plant and
become thickened and form tubers at their tips ; at the end of
the summer the parent plant dies and leaves only the tubers,
which in the following year develop into new separate plants.
Almost all plants with underground branching rhizomes behave
in a similar manner ; the older main portions die off and leave
the young lateral rooted branches to carry on their existence
as separate individuals.
The buds on the stolons or runners of the strawberry and
creeping crowfoot (Fig. 21) become rooted to the ground
258
CUTTINGS 259
and after the death of the bare internodes form separate
plants.
Other examples of vegetative multiplication are seen in the
growth of bulbous and corm-bearing plants (pp. 56-60).
3. In addition to the natural modes of reproduction just
mentioned, various artificial modes of vegetative propagation
are known. Detached pieces of the roots, stems or leaves of
many plants when placed under certain conditions indicated
below, give rise to those organs which are necessary to make
the part a complete plant : thus the shoots of plants when cut
off and placed in suitable soil soon develop a system of ad-
ventitious roots, and pieces of roots treated in a similar manner
produce buds from which leafy shoots arise. It is a remarkable
fact that although roots may be formed when either end of a
cutting is inserted in the earth, the best development of roots
always takes place when that end of the cutting which was nearest
the root of the parent plant is buried in the soil. Also when a
root-cutting is buried in the ground, the greatest growth of roots
originates from that end of the cutting which was nearest the apex
of the root, the other end giving rise to adventitious buds. The
severed shoots of certain conifers and other plants do not appear
to be able to form roots, nor are their roots capable of forming
buds : plants such as these cannot be reproduced vegetatively.
The commonest examples of artificial vegetative reproduction
are seen in the propagation of plants by means of cuttings and
layers and in the processes of budding and grafting so extensively
practised by nurserymen and gardeners.
4. Cuttings. The term cutting is applied to any portion of a
root, stem or leaf cut from a plant and used for propagation.
A few plants, such as pelargoniums, have the power of forming
adventitious buds upon cut portions of their roots, and may be
propagated by root-cuttings. The leaves x)f gloxinias, begonias
and other plants, when cut through the midribs and fastened
down or merely laid on damp sand, and kept at a suitable
260
REPRODUCTION
temperature, produce buds and roots which develop into new
plants at points where the midribs are cut.
In the majority of cases, however, shoots are selected for
cuttings : tHey generally give best results
when cut through just below a node, for in
most instances it is only at the latter points
that adventitious roots are formed. Those
of leafy herbaceous plants are placed in
loose, warm soil to induce a rapid formation
of roots and are kept in a somewhat close
damp atmosphere to prevent too rapid loss
of water by transpiration during the time that
the shoots are without roots.
Woody cuttings contain a sufficient store
of food for the formation of callus-tissue
and roots : herbaceous cuttings, however,
usually possess but very small amounts of
ready - formed plastic materials and must
therefore be exposed to light so as to carry
on the work of * carbon-fixation.'
Currants, gooseberries and vines are very
readily increased by cuttings : pears and
apples may also be reproduced in a similar
manner, but the production of roots by the
shoots of these trees is very uncertain.
The cuttings of fruit trees are usually
8 or 10 inches long and taken from well-
matured wood of the previous season's
growth, after the shoots have lost their
leaves in autumn. The buds on the portion
of the shoot inserted in the soil should be
cut out where 'suckers' are to be avoided,
and only the buds needed for the formation of the bush or tree
left on the part above ground (Fig. 91).
FIG. 91. Cutting
of gooseberry showing
formation of adventi-
tious roots below
ground.
LAYERS
261
In the apple and pear, roots form more readily when the
cuttings include a ' heel ' or small basal piece of wood from the
older branch on which the cutting originally grew.
Hops are propagated by cuttings (p. 344), and the tubers of a
potato when very large or the variety a scarce one are sometimes
cut longitudinally so that each piece possesses an 'eye' or
collection of buds which develops into a new plant when the
piece is placed in the ground.
5. Layers. The process of layering consists in bending and
pegging down a shoot of a plant into the soil as indicated in
Fig. 92. From the bent por-
tion in the earth roots are
sooner or later emitted, after
which the shoots spoken of as
layers may be severed com-
pletely from the parent plant.
The mere bending and cover-
ing the shoot with moist warm
soil is sometimes sufficient to
induce the emission of roots,
but more generally one or other
of the various plans of ' tongue-
ing,' 'ringing,' and ' notching,' must be adopted to secure a good
formation of root.
'Tongueing' is a term applied to the process of cutting an
oblique slit upwards as at a almost through the stem at a node.
'Ringing 7 (b) consists in removing a complete half-inch wide
ring of bark or tissues as far as the cambium of the stem : by
'notching' is meant the cutting of a V-shaped incision half
through the stem. All these devices and others which are
practised retard the flow of elaborated sap backward from the free
portion of the shoot above ground, and the consequent accumula-
tion of plastic material in the part of the shoot beyond the cut
tends to induce the formation of adventitious roots upon it.
FIG. 92. Diagram illustrating method
of layering, b Ringed branch ; a. tongued
branch.
262 REPRODUCTION
Layering is usually more successful than propagation by
cuttings, for the latter are liable to die before a root-system is
developed adequate to their requirements : in the process of
layering the shoot remains attached to the parent until it is
rooted, during which time it derives its water-supply and a
certain amount of food from the latter.
Currants and grapes are readily increased by layers, and the
process is adopted for the rapid production of apple, pear, plum,
quince and other stocks which are subsequently employed for
budding and grafting purposes. The layering of these usually
takes place in autumn, the layers being left attached to the
parent about twelve months or until a satisfactory root-system
is developed, after which time they may be completely severed
from the parent and planted out.
6. Budding and Grafting. In the process of budding^ a bud is
taken from one plant and inserted into the stem, or stock as it is
termed, of another; ingrafting a portion of a shoot with several buds
upon it is treated in a similar manner. The shoot, which in the
grafting process is inserted into the stock, is termed a graft or scion.
The inserted bud and stock or the scion and stock when
properly treated become organically united with each other and
behave as one plant. The roots of the stock supply the bud or
scion attached to it, with water and other ingredients from the
soil, and the leaves of the shoots developed from the bud or
scion elaborate plastic material for the nutrition and growth of
the root. Nevertheless, in nearly all cases the scion and stock
preserve their own individual morphological peculiarities, and
in this respect behave as distinct, separate plants.
It is stated that in some instances budded or grafted plants
give rise to shoots which in form of leaf, colour of their flowers,
and other morphological characters, resemble those of the scion
and those of the stock as well. Shoots produced in this manner
with such blended characters are described as graft-hybrids-,
they are of very rare occurrence.
BUDDING AND GRAFTING 263
Budding and grafting are processes mostly applied in practice
to woody dicotyledons; herbaceous plants may, however, be
made to unite satisfactorily. Attempts to graft monocotyledons
with each other rarely succeed.
One species of plant can often be successfully grafted on a
totally distinct species, as, for example, the peach on the plum,
the apple on the pear, the pear on the quince, and the tomato
on the potato. Moreover, certain species belonging to different
genera unite and grow satisfactorily, as the medlar on the
hawthorn, and the Spanish chestnut on the oak. Apparently,
however, only plants can be grafted on each other successfully
when they belong to the same Family or Order.
Although a variety of pear, whether grafted on the quince,
apple, wild pear or other stock, remains a pear and possesses
all the special characters for which it is grown, the scion is
nevertheless influenced in the size and flavour of its fruit, in
the earliness or lateness of its fruit-bearing power, its habit of
growth, and in other ways, by the stock on which it is grafted.
Similar influence of the stock on the scion and its produce, is
observable in most other fruit trees, and appears to be connected
with the mechanical difficulty of transport of the food material
through the wood at the point of union of stock and scion.
Fruit trees on their own roots are less fruitful and the fruit is
of poorer quality than that obtained from the same variety of
tree grafted on another appropriate stock.
For the production of dwarf trees which fruit at an early age
the pear is usually grafted on the quince and similarly the apple
is grafted on the so-called ' Paradise ' stock, a name given to
certain surface-rooting dwarf varieties of apple.
Where larger trees are required which do not fruit so soon but
which are of greater longevity than dwarfs, the pear is grafted on
stocks raised either from seeds of the wild pear or from common
varieties of pear used in the manufacture of perry, and the apple
is grafted on stocks raised from seeds of the crab or wild apple,
264
REPRODUCTION
or upon the so-called Free stocks raised from seeds of cider
apples.
Heart and Bigarreau varieties of cherry are budded and grafted
on seedlings of the Wild Gean (Prunus Avium L.), the Morello
and Duke types being inserted on stocks of Dwarf cherry (Prunus
Cerasus L.).
Mussel and St Julicn plums are frequently used as stocks for
plums. A great many different ways of preparing and inserting
the buds and scions are practised.
In the propagation of fruit trees and roses by budding, the
commonest method is that known as shield-budding, which is
usually performed in July or August when the bark of the stock
can be readily separated from the wood along the active
cambium-ring. The buds selected for insertion must, of
course, be wood buds, and are taken from shoots produced
in the same year. They
must not be too young
nor too old, and are
therefore cut from the
middle portion of the
shoot where the wood
is about half-ripe.
The bud to be used
is cut from the young
shoot in the manner in-
dicated at a /;, Fig. 93 :
a shield-shaped piece
of the bark is removed
with the bud, and also
a small portion of the
wood of the shoot, which
F|G - 93 ' must be carefully pulled
from the bark and thrown away. If in withdrawing this small
piece of wood the rudimentary vascular cylinder or axis of the
BUDDING AND GRAFTING
265
bud comes with it, the bud appears hollow when viewed from
inside and is useless, for it cannot develop. The leaf in whose
axil the bud is growing is severed as at x so as to leave about a
quarter of an inch of petiole attached to the bark. This done
a T-shaped incision (A, Fig. 94) is cut in the stock and the
bark gently raised as at B : the prepared bud is then inserted
in the slit as at D and the whole firmly tied round with raffia-
grass or cotton-wick so as to press the wounded parts together,
leaving the bud itself exposed (E, Fig. 94).
FIG. 94. Diagram illustrating a common method of ' Budding.'
The bandage should be removed or released in about three
weeks or a month after budding, and after the upper part of the
stock has been cut off in autumn no growth except that from
the inserted bud should be allowed.
In budding operations carried out as above, the healing-tissue
or callus formed by the cambium of the transplanted bud becomes
united with that formed by the cambium of the stock upon
which the bud is placed, and as the cambial surfaces brought
266
REPRODUCTION
together are comparatively large, a good union is very readily
made.
In the process of grafting a short piece of a shoot with from
two to four buds upon it is united with the stock.
In the grafting of fruit trees the grafts or scions are cut in
January or February before vegetative growth commences, from
well-ripened shoots of the preceding year's growth. They are
then placed in moist sand or garden soil on the north side of a
wall, or kept in a cool cellar in order
to prevent them from drying up and
to keep them dormant until they are
needed in March or April when the
actual operation of grafting is generally
carried out.
The upper part or ' head ' of the tree
or stock is cut off completely at a
point a little way above where the
scion is to be grafted. This prepara-
tion of the stock must be done before
growth begins in spring, the best time
being usually in the early part of
February.
Very numerous methods of uniting
the scion to the stock are practised by
gardeners and nurserymen.
In all cases it is important to re-
member that the callus or healing-
tissue which brings about the union,
arises chiefly from the cambium of the scion and stock and the
cells immediately bordering on the cambium : the old matured
portion of the wood takes no part in the process.
The commonest modes in use are tongue- or whip-grafting
and rind- or crown-grafting, the former being largely adopted
where the scion and stock are approximately the same in thick-
FIG. 95. Diagram illus-
trating mode of tongue-graft-
ing. I. Stock a and scion b
separate. II. The same fitted
together before being bound
and waxed.
BUDDING AND GRAFTING
26 7
ness, the latter where the scions are grafted upon much thicker
branches and stems.
In tongue-grafting the scion is first cut with a long sloping cut
2 or 3 inches long, and then notched as at , Fig. 95. The stock
is treated in a similar manner so that when placed together the
scion and stock fit as at II, Fig. 95. The two parts are subse-
quently bandaged firmly, and the wound
covered either with grafting-wax or clay
to exclude air and rain.
As soon as the buds on the scion have
grown into shoots 6 or 8 inches long the
bandages and covering should be care-
fully removed, and the scion and stock
tied to a supporting stake.
In crown-grafting one or more scions
are cut with long sloping cuts and then
inserted into longitudinal slits 2 inches
long, cut through the bark of the stock
as shown in Fig. 96. The wounded
parts are then bound and covered with
clay or wax as in tongue-grafting.
The growths from bulbs, tubers, cuttings,
grafted buds and scions are, strictly speak-
wuh three scions inserted. ing> nQt new p } ants> but Simple CXten-
sions of the body of the parent which produced them : with
rare exceptions, they possess the same morphological and
physiological characters as the plant from which they were
derived. Whatever qualities the parent possesses which make
it valuable, the same are met with in the plants derived from
it by the various methods just described, and it is largely on
account of this fact that the farmer, gardened, and nurseryman
makes use of the power of vegetative reproduction. ,
Plants raised from the seeds of choice varieties of apple, pear,
cherry and other fruit trees usually differ very widely from their
a
FIG. 96,-Diagram iiius-
268 REPRODUCTION
parents, and the same want of resemblance between parent and
offspring is seen when seedlings of carnations, chrysanthemums,
dahlias, potatoes, hops, and a vast number of other cultivated
plants are compared with their progenitors.
The reproduction of plants by seeds cannot, therefore, in such
cases, be relied on as a means of obtaining a number of
examples all resembling their parent : the only method of
obtaining the desired result is to take advantage of the power
of vegetative reproduction.
Another reason for the employment of the power of vegetative
reproduction is the great saving of time which is effected when
the rapid multiplication of certain kinds of plants is the object in
view. To raise a remunerative crop of potatoes from true seeds
would take five or six years, and an even greater time would be
needed to produce an orchard of fruitful trees from the ' pips '
of pears or apples : by the use of tubers in the former, and by
grafting on well-established stocks in the latter cases, the end is
attained in a comparatively short time.
The same saving of time is seen in the raising of strawberries
from separated runners instead of seeds, and in the propagation
of tulips, hyacinths, and narcissi by means of bulbs rather than
by seeds.
Ex. 162. Examine cuttings and layers ol carnations, pelargoniums, goose-
berry, black-currant and any others obtainable after they have rooted. Make
drawings of the rooted ends.
Ex. 163. All students should be required to bud a rose and graft a fruit
tree of some kind.
Examine the external feature of budded and grafted trees in orchards
and gardens. Notice it' the stock and scion grow ifl thickness at the same rate.
CHAPTER XXII,
REPRODUCTION (continued}.
SEXUAL REPRODUCTION.
i. THE essential feature of the sexual reproduction of plants
and animals also, is the fusion of two special kinds of cells,
namely, a male reproductive cell, and a female reproductive
cell, which after complete coalescence or commingling of parts,
give rise to a single cell capable of growing into a new organism.
In the very exceptional cases of parthenogenesis > a female ceil
develops into a new plant without previously uniting with a
male cell ; as a rule, however, neither a male cell nor a female
cell is capable of further development by itself, and it is only
after the process of fertilisation or union of the male cell with
the female cell that the latter grows into a new individual plant.
The two uniting cells, or gametes as they are termed, are
produced in special reproductive organs which vary very much
in different divisions of the Vegetable Kingdom. We can, at
present, only deal with the sexual cells and reproductive organs
of ordinary flowering plants.
The reproductive organs of these plants form the essential
parts of flowers as mentioned in chap. vi. ; the stamens are
the male organs and the carpels the female organs of the
plant.
The male reproductive cell is enclosed within the pollen-grains
produced in the stamens : the female reproductive cell lies with-
in the ovule as explained below.
2. Structure and Germination of the Pollen-Grain. Pollen-
grains vary much in form, size and colour: they are, however,
270
REPRODUCTION
generally oval or spherical bodies of a yellowish colour. The
exterior of the grain usually consists of a stout cuticularised
cellulose coat the exine
often elaborately ornamented
"with spiny, wart-like, or net-
like thickened markings ; here
and there more or less de-
finitely arranged, thinner areas
are visible on the coat. Lining
this outer protective covering
is a delicate transparent cellu-
lose membrane the intine
(Fig. 97). The interior of the n-
grain is filled with cytoplasm,
in which are present two nuclei,
representing two cells, between
... . . . . . , . FIG. 97. i and a. Pollen-grains of a species
Which there IS nO dividing of hly, with netted exine, on which small drops
i, ,i s\ r 1.1. / \ ^ Ol1 are visible. 3. Section of a pollen-grain :
Cell- Wall. Une Ol them () a exine; b inline ; v nucleus of the vegetative
cell ; g nucleus of the generative cell. 4. Ger-
minating
is the generative Cell y the minating pollen-grain; ^/ pollen-tube; r nucleus
/ v i , j ,1 of the vegetative cell; eg two male nuclei
Other (V) being termed the produced by division of the nucleus of the
vegetative cell of the pollen- generative cclh
grain. Within the cytoplasm, starch, sugar, oil and other food
materials can often be recognised.
When a pollen-grain is placed in a weak solution of sugar, and
kept at a suitable temperature, it absorbs water, and emits a
closed slender tube-like structure, termed the pollen-tube (//), which
grows from the vegetative cell of the grain, and may under certain
conditions attain a length of several millimetres. The pollen-tube
is a protrusion of the intine, and makes its way through the
specially thin or otherwise modified places in the exine of the
grain.
During the germination of the pollen-grain the two nuclei
present in it travel into the pollen-tube; the nucleus of the
vegetative cell ultimately becomes disorganised and disappears,
THE OVULE AND ITS STRUCTURE 271
but the nucleus of the generative cell divides into two portions
(g g, 4, Fig. 97), the male gametes or male cells^ which take part
in the fertilisation-process described hereafter.
Ex. 154. Shake out, or otherwise transfer to a dry slide, pollen -grains
from the anthers of shepherd's-purse, sunflower, cucumber, dandelion, apple,
mallow, sweet-william, tulip, and any other flowers at hand.
(1) Examine with a low power, allowing the light to fall on them from above.
Note the colour, and sketch the form and arrangement of the markings on
the outer wall.
(2) Mount a few of each of the pollen-grains in water or alcohol, and
examine with both a low and a high power.
Ex. 165. Make a 3 per cent., 5 per cent., and a 10 per cent, solution of
cane-sugar; place some of each in separate watch glasses, and shake into
them various kinds of pollen-grains. Cover each watch glass with another,
and keep the whole in the dark in a warm room. Examine with a high
power some of the pollen-grains from each glass after twelve or eighteen
hours, and note the production of pollen-tubes from many of them.
3. The ovule and its structure. As previously explained in
chapter vi. (p. 85), the ovules are minute roundish or egg-
shaped bodies found in the ovary of the carpels of a flower. In
most cases each ovule is attached to the placenta of the carpel
by means of a short stalk orfunicle.
The chief part of an ovule consists of a central kernel of thin-
walled parenchymatous tissue termed the nucellus (n, Fig. 98).
Surrounding the latter are one or two coats or integuments (c)
which have grown up from the base of the nucellus so as to
cover it completely except at its apex where a very narrow
canal (m) the micropyle is left.
The ovules of umbelliferous plants and most dicotyledons with
gamopetalous flowers have only a single integument; those of
the monocotyledons and most apetalous and polypetalous dico-
tyledons possess two integuments.
The point (h) where the coats and the tissue of the nucellus
are united is termed the chalaza of the ovule.
Various forms of ovule are met with in different kinds of
flowering plants. In the dock, walnut and buckwheat, the funicle,
19
272
REPRODUCTION
chalaza and micropyle are all in the same straight line, as at
i, Fig. 98 : such ovules are described as orthotropous .
When the ovule during its development becomes inverted as
at 2, Fig. 98, the micropyle lies close to the funicle : this form
is met with in the majority of common flowering plants, and is
spoken of as an anatropous
ovule. Among cruciferous
plants, and also among the
Caryophyllaceae and Cheno-
podiaceae, the ovules are
more or less kidney-shaped,
the nucellus and integu-
ments being curved or bent : ,.
ovules of this type are-/
described as campy lotropous.
At an early period in the
development of the ovule a
specially large cell termed
the embryo-sac makes its ap-
pearance in the tissue of the
nucellus at a point near the
micropyle of the ovule.
Within it a series of seven
new cells are developed
somewhat as follows. The
primary nucleus of the
embryo-sac first divides, and
the two halves then travel
to the poles or opposite ends
of the cell, one to the micro-
pylar end, the other to the antipodal or chalazal end. Here each
of these two new nuclei divides into four, so that at this stage eight
nuclei are present, each of which has a certain portion of cytoplasm
associated with it. After this, one of the nuclei from the chalazal
-ft
FIG 98 i. External view of an orthotro-
pous ovule. 2. The same of nn anatropous
ovule. 3. Longitudinal section of i. 4.
Longitudinal section . of 2. / Funicle ;
m micropyle ; h chala/a ; C coats of ovule ;
n nucellus ; t embryo-sac.
FERTILISATION AND ITS EFFECTS 273
end and one from the micropylar end travel back to the centre
and fuse with each other to form what is termed the secondary^
definitive^ or fusion nucleus of the embryo-sac (h, Fig. 99) : it is
fat primary endosperm nucleus.
The three nuclei at the end of the embryo-sac farthest away from
the micropyle become surrounded with a certain amount of cyto-
plasm and then develop cell-walls ; the cells produced are termed
antipodal cells (a). At the end nearest the micropyle the nuclei
and associated cytoplasm remain without cell-walls and constitute
what is known as the egg-apparatus ; two of these three cells are
termed synergidce, the third is the female gamete^ ovum, egg or
oosphere(e). The ovum is the special female reproductive cell of the
plant which after fusion with the male reproductive cell ofthepollen-
grain, begins a new life as it were, and develops into a new plant.
Ex. 166. Tease out with needles the ovules from the ovaries of the recently
opened flowers of pea, bean, tulip, and others of similar size ; Amount in a drop
of water and examine with a low power, noting if possible the funicle and
position of the micropyle.
Ex. 167. Cut transverse sections of these ovaries and mount the sections
in a i per cent, solution of caustic potash. Observe and sketch under a low
power the form, structure and attachment of the ovules to the carpels.
Ex. 168. Place some flowers of marsh marigold (Caltha palustris L.)
which have just opened in methylated spirit, After hardening a few days
strip off the petals and stamens and cut a number of transverse sections
through the carpels with a razor wetted with the spirit ; many of the sections
will also pass through the ovules within the carpels. Transfer the sections
into a watch glass containing a mixture of equal parts of methylated spirit
and glycerine. Now pick out one or two sections which appear to have
passed through the ovules and mount them in a drop of pure glycerine.
I. Examine and sketch under a low power, noting
(1) The section of the wall of the carpel ;
(2) The anatropous ovule and its funicle ;
(3) The large embryo-sac.
a. Examine and sketch the embryo-sac under a high power, noting
within it
(i) The central fusion nucleus ;
(2) The antipodal cells at one end ; and
(3) The ovum and synergida at the other.
4. Fertilisation and its effects. When a pollen-grain is placed
on the stigma of the carpel of a suitable flower it germinates
274
REPRODUCTION
St
and produces a pollen-tube which penetrates into the tissues of
the stigma and grows down through the style into the cavity
of the ovary : the time taken to reach this point may vary from
a few hours to several weeks, according to the kind of plant
The advancing pollen-tube is
guided in some way not completely
understood into the micropyle of the
ovule and at length comes into con-
tact with the apex of the embryo-sac
close to the egg-apparatus (Fig. 99).
On reaching this point its tip be-
comes disorganised and one of the
male cells of the pollen-grain travels
on through the open end of the tube
S until it meets the ovum. The male
-K gamete and the ovum then fuse into
one, their parts becoming com-
pletely intermingled. This fusion
^ of a male cell with the ovum is the
I essential feature of the sexual act
and is spoken of as fertilisation.
In several instances the second
male nucleus from the pollen-grain
has been found to fuse similarly with
the fusion nucleus in the embryo-sac.
The fusion of both male cells, one
with the egg, the other with the
primary endosperm nucleus, has
been referred to as double, fertilisa-
f
FIG 99 Diagram of a longitudinal
section of a carpel containing an ortho-
tropous ovule: designed to illustrate
the arrangement of the various parts
about the time of fertilisation, o Ov-
ary ; s style ; st stigma of the carpel ;
^ pollen-grain germinated on the
stigma; // pollen-tube; r one of the
male gametes ;/funicle; M chalaza; //^ . ft J s general among angio-
c integuments of ovule ; n nucellus ;
r /embryo-sac, /ovum or egg; A fusion-
nucleus (primary endosperm nucleus) ;
a antipodal cells.
sperms.
Unless the ovum is fertilised both
it and the whole ovule wither and die, but as soon as fertilisation
is effected the ovum commences to divide and grow, developing
into an embryo plant, the whole ovule finally becoming a seed.
FERTILISATION AND ITS EFFECTS 275
The development of the embryo of a dicotyledonous plant
from the fertilised ovum may be easily studied in the common
weed ShepherdVpurse (Capsella Bursa-pastoris L.).
The ovum first surrounds itself with a cell-wall and subse-
quently divides into two cells : of these, the upper one or that
nearest the micropyle, by further transverse divisions gives rise to
a single row of cells termed the suspensor (j, Fig. 100). The other
FIG. 100. i. Diagram of ovum. a. The same after first division. 3 and
4. Suspensor (f ) and embryo-cell (e) of Shepherd's-purse ; in 4 the embryo-
cell (e) has undergone division ; A, hypophysis. 5. Later stage of the de-
velopment of the embryo, showing portion of the suspensor still attached
to it ; d dermatogen ; periblem ; p plcrome of embryo. 6. Fully-formed
embryo ; r its radicle ; c two cotyledons.
or lower spherical cell (e) is carried at the end of the suspensor
some distance into the cavity of the embryo-sac ; it is spoken
of as the embryo-cell since from it the whole of the embryo is
developed except the tip of the radicle and the root-cap.
The single embryo-cell divides in three directions so that eight
cells are formed : four of these nearest the suspensor by continued
division produce the hypocotyl and radicle, while the other four
give rise to the cotyledon and plumule of the embryo. The
276 REPRODUCTION
tip of the radicle and the root-cap originate by division of the
hypophysis, or end cell (h) of the suspensor,
BT T 169. Pull off from an inflorescence of Shepherd's-purse (Capsella) an
ovary of a flower from which the petals have just fallen. Open the ovary
with needles and remove a few of the ovules : place one or two of the latter
in a drop of water on a glass slide and cover with a cover-slip.
(1) Examine with a low power and sketch the parts of a single ovule and
its funicle.
(2) Press gently on the cover-slip with the end of a lead pencil, so as to
burst the ovule : try and find with a low power the embryo and suspensor, as
at 3 or 4, Fig. 100, among the contents squeezed out. When found examine
and sketch under a high power.
(3) Repeat the above with ovules obtained from successively older ovaries,
and trace the development of the embryo up to the time when well-marked
cotyledons and radicle are clearly visible with a low power.
At the same time as the development of the embryo is going
on, changes occur in other constituents of the embryo-sac and
also in the nucellus of the ovule. The synergidae and the anti-
podal cells usually become disorganised and disappear. The
primary endosperm nucleus of the embryo-sac, however, unites
with one of the male gametes from the pollen-grain and the com-
pound nucleus arising from such union divides repeatedly until
a large number of naked cells are produced, between which cell-
walls ultimately arise, the whole then forming a parenchymatous
tissue within the embryo-sac : this tissue is termed the endosperm
(e, Fig. 10 1 ) and is stored with food on which the embryo lives
during its development.
In wheat, barley, onion and other species of plants the embryo
does not disorganise and consume all the endosperm before the
seed ripens, so that in these cases a certain amount of endosperm
is present in the mature seed (3, Fig. 101).
In others, however, such as the bean, pea, and turnip, the
developing embryo absorbs practically the whole of the endo-
sperm and the nucellus before the seed ripens, so that mature
seeds of these plants contain little or no endosperm-tissue and
are described as exendospermous (4, Fig. 101).
Most commonly the tissue of the nucellus is disorganised
and absorbed during the development of the embryo, but in
FERTILISATION AND ITS EFFECTS 277
certain plants it becomes stored with food and is present in the
ripe seed: such stored nucellar tissue is termed pcrisperm (n, 2,
Fig, 10 1).
The fertilisation act brings about the production of an embryo,
and stimulates the growth of other parts of the ovule, so that
r
FIG. ioi. Diagrammatic longitudinal sections of an ovule (i) and the seeds (2, 3, and 4)
which may be derived from it.
x The ovum which after fertilisation becomes the embiyo of the seed j tn micropyle ;
ch thalaza ; f funicle ; / coats of ovule | embryo-sac; n nucellus .' r radicle of embryo ;
c cotyledons of embryo.
2 and 3 are 'albuminous' seeds, tissues derived from the nucellus and embryo-sac being
present in them. In 2 the tissue n is termed perisperm ; it is absent from 3. In 3 the
endosperm tissue e produced within the embryo-sac is alone present with the embryo.
4 U an ' exalbuminous ' seed, both penspeim and endosperm being absent.
the latter is finally converted into a seed: the corresponding
parts of the ovule and the seed are indicated below :
The Ovule. The Seed.
The egg or ovum becomes the embryo,
integuments seed-coats or testa.
micropyle micropyle.
funicle funicle.
In so-called ' albuminous ' seeds, the * albumen ' may re-
present storage-tissue developed in the embryo-sac and termed
endosperm, or it may be derived from the nucellus, in which
278 REPRODUCTION
case it is designated perisperm ; some seeds may contain both
endosperm and perisperm.
After fertilisation has been accomplished, the style and stigma
of the carpels and also the corolla of most conspicuous flowers,
wither and fall off. The stimulus of the sexual act incites the
ovule to grow, and a similar influence is transmitted to the
tissues of the ovary- wall, which also grow and expand to allow
the development of the seeds within : the gynaecium of the flower
becomes converted into a fruit.
Moreover, the act of fertilisation frequently induces growth
and change in the receptacle and flower-stalk, as in the apple,
pear, and strawberry.
Some cultivated plants, such as varieties of cucumber, grape,
pine-apple, orange, and banana, produce 'seedless fruits,* the
walls of the ovaries developing extensively apart from any seed
production. However, in the tomato, melon, plum, and the
majority of plants, fruits either do not develop at all or drop
off long before they reach normal size, when fertilisation does
not take place.
That the development of the seed influences the growth of
the fruit may be seen by watching the development of an
apple flower in which some of the five stigmas present have
been pollinated and others left : the * fruit * from such an
incompletely pollinated flower becomes somewhat one-sided
and unsymmetrical in form, for only the carpels corresponding
to the pollinated stigmas produce seeds, and it will be found
that the part of the ' fruit ' in which the seeds a*re present grows
more rapidly than the seedless part.
Tomatoes and strawberries also develop into one-sided,
irregular fruits when pollination is incomplete.
Only one pollen-grain is necessary to fertilise a single ovule,
and more pollen is always produced by flowers than is absolutely
necessary for the impregnation of all the ovules within their
carpels. There is however some evidence to believe that when
THE FORMATION OF GAMETES 279
an excess of pollen is applied to the stigmas of flowers, the tissues
of the pericarp are stimulated to develop more extensively, and the
fruit is consequently larger than when a small amount of pollen
is applied.
5. The formation of gametes : meiosis, or the reduction
division. As already explained, in the fertilisation process two
reproductive cells, namely, a male gamete from the pollen-grain
and the female gamete or ovum in the ovule, unite to form a
single cell, which divides by the ordinary process of mitosis, first
into two cells, and then similarly again exactly as in the division
of the vegetative cells of root-tips and growing-points of stems
described previously (p. 269).
It is clear that if the uniting gametes contain the same number
of chromosomes as the rest of the cells of the body of the plant
producing them, the fertilised ovum will have within it twice as
many chromosomes as the cells of the parent plant, and all the
cells which develop from the fertilised ovum will likewise have
double the number of chromosomes ; similarly, the chromosomes
in the cells of plants would be again doubled in each succeeding
generation.
It is found, however, that the number of chromosomes remains
constant from generation to generation, a result due to the fact
that the nuclei of the uniting gametes contain only half the
number present in the rest of the cells of the plant. This reduced
number in the gametes is brought about in the manner described
below.
Mitosis, with longitudinal splitting of the chromosomes goes on
in all cells of the plant up to the period when the pollen grains,
or microstores, begin to form in the stamens and the embryo sac
arises in the ovule.
The pollen-mother cells from which the male gametes are pro-
duced, like all other cells of the plant, possess the unreduced
number, 2w, of chromosomes (termed the diploid or double number),
but at the first division of such cells the individual chromosomes,
instead of splitting longitudinally into two halves as in mitosis,
come together undivided in pairs in the equatorial region of the
cell (3, Fig. ioia). The individuals of the different pairs then
separate from each other, half of them (the haploid or single
number n) going to one pole of the cell, the other half to the
opposite pole.
The two opposing groups, each containing half the number of
REPRODUCTION
Fio ioia. Diagram of Meiosis, or reduction division of pollen mother-cell, i. Mother-
cell, with resting nucleus. 2. Cell showing four chromosomes (the unreduced double, or
dvploid number) in the nucleus. 3. The four chromosomes forming two pairs on equatorial
plate of the cell. 4. Separation of whole chromosomes. 5. Daughter-cells of the first (the
reducing) division, the nucleus of each with two chromosomes (the reduced, single or haploid
number). 6. Mitosis of the two daughter-cells. 7. Resulting four cells, each with nucleus
containing the reduced number of chromosomes. 8. Four fully formed pollen grains
(microspores) arising from pollen mother-cell x.
SEXUAL REPRODUCTION
2796
PIG. loift. Diagram of gamete formation in the pollen grain, i. Pollen grain with two
chromosomes in nucleus. 2, 3, 4. First mitotic division of nucleus giving rise to two nuclei,
each with two chromosomes, one the nucleus of the vegetative cell, the other the nucleus
of the generative cell of the pollen grain. 5, 6, 7. Mitosis of nucleus of the generative cell.
8. Pollen grain with resting nucleus of the vegetative cell () and two male gametes (f).
279'
REPRODUCTION
SEXUAL REPRODUCTION 279^
FIG. xoic. Diagram of meiosis and gamete formation in the embryo sac mother-cell.
x. Mother-cell of embryo sac or macrospore, with resting nucleus. 2. Nucleus of i with
four chromosomes (the unreduced diploid number). 3. Pairing of whole chromosomes on
the equatorial plate. 4. Reduction division complete, with formation of two cells (potential
embryo sacs) each with two chromosomes (the reduced haploid number). 5. Embryo sac
with resting nucleus. 6. Nucleus showing the reduced (haploid} number (2) of chromo-
somes. 7, 8. First mitotic division of embryo sac, with production of two reduced nuclei.
9. Cell with four nuclei, the result of mitosis of 8 (the second mitotic division of the nucleus
of the embryo sac nucleus). 10. Third mitotic division with production of eight nuclei.
IT. Embryo sac ready for fertilisation ; o, ovum or female gamete ; s, synergidaa ; a, anti-
podal cells ; d, primary endosperm nucleus, or ' fusion ' nucleus of embryo sac with four
chromosomes (the diploid number) derived from the fusion at the centre of one cell from
each of the two groups of four at the poles of 10 ; p, pollen tube with two male gametic
nuclei, one of which on fusion with the ovum, gives fo t the fertilised ovum, from which a
new plant develops with the full double complement of chromosomes in each cell, the
other male nucleus combining with the primary endosperm nucleus, which later gives rise
by mitosis to endosperm tissue, each cell of which contains an extra set of chromosomes.
chromosomes of the parent cell, ultimately become incorporated
in the two new nuclei of the daughter-cells ; each daughter-cell,
therefore, contains the reduced (haploid) number of chromosomes,
and the division which leads to this result is termed meiosis, or
the reduction division.
Later, these two cells, each with the reduced number, divide
mitotically as in ordinary vegetative cells, giving rise to four cells
which without further nuclear changes develop into pollen-grains
(Fig. ioia).
It is within the pollen-grains that the male galetes are formed
after two mitotic divisions as illustrated in Fig. ioi&.
A reduction division, similar to that described in the production
of a microspore or pollen-grain, precedes the formation of the
macrospore or embryo sac, within which the female gamete or
ovum is produced.
The nucleus of the macrospore mother-cell, like that of the
microspore mother-cell, contains the unreduced (diploid) number
of chromosomes (Fig. loi^r). At division, pairing of whole chromo-
somes occurs, with subsequent separation of the individuals of
each pair into two reduced (haploid) groups, exactly as in the
reduction division of the pollen mother-cells. (Compare 1-7,
Fig. ioia, and 1-4, Fig. ioic).
The reduction division of the embryo sac mother-cell results
in the formation of two daughter-cells, both potential embryo
sacs, each containing the reduced (haploid) number of chromo-
somes. This is usually followed by a mitotic division of the two
cells, and a longitudinal row of four cells appears ; usually only
one of these functions as an embryo sac or macrospore, the other
three degenerating.
It is after three more mitotic divisions of the nucleus within the
embryo sac that the female gamete or ovum arises as illustrated
in 5-11, Fig. ioic.
It must be observed that while the reduction divisions bring
about the production of cells each with half the number of
chromosomes present in the parental cell, it is only after two or
three mitotic divisions of these cells that the actual gametes
which take part in fertilisation are produced.
In the fertilisation process one of the male gametes, with its
reduced number of chromosomes (n\ unites with the ovum of the
embryo sac, giving rise to the fertilised ovum with a full comple-
ment of chromosomes (2). From the latter a new plant develops
POLLINATION 2797
by repeated mitosis, producing a seedling in each cell of which
there is the same number of chromosomes (2n) as in those of the
parent plant.
The second male gamete from the pollen-grain combines with
the fusion nucleus of the embryo sac (' double fertilisation '),
adding to it a third set of chromosomes ; leading to the formation
of the primary endosperm nucleus. The latter is in reality the
product of a triple fusion of one paternal with two maternal
nuclei, which on repeated mitosis gives rise to the endosperm
tissue, each cell of which contains $n chromosomes (n, Fig. ioic}.
6. Pollination : self- fertilisation and cross- fertilisation. It
will be understood from the foregoing account that among plants
with completely closed carpels the fertilisation-process is preceded
by and dependent upon the deposition of the pollen-grain on the
stigma of the carpel of a flower. Although the pollen-grains
may be induced to germinate on other parts of the carpel, the
pollen-tubes have no power of penetrating the tissues of the
latter except when placed on the specially receptive stigma.
This necessary transference of pollen-grains from the anthers of
the stamens to the stigmas of the carpels is termed pollination.
Where the stigma receives pollen from the anthers of the same
flower the latter is said to be self -pollinated : frequently, however,
the stigma in one flower receives pollen from a flower growing
on another distinct plant, in which case the flower receiving the
pollen is spoken of as cross-pollinated.
A simple term is needed for the intermediate case where the
pollen of a flower is transferred to the stigma of another flower
growing on the same plant.
Where self-pollination is followed by fertilisation the plants
are said to be self-fertilised or close-fertilised ; the term cross-
fertilisation is applied to cases where the fertilising pollen is
derived from another distinct flower of the same species of
plant.
Since most plants have their sexual organs close together in the
same flower it might be imagined that self-fertilisation would be
the rule among flowering-plants. A number of plants with open
flowers are undoubtedly self-fertilised and certain plants such
as pansy, violet, wood-sorrel and barley, possess cleistogamous
flowers which never open and which therefore insure certain
self-fertilisation.
Extensive and careful observation, however, shows that a large
280 REPRODUCTION
number of flowering plants are cross-fertilised, and experiments
have proved that the plants derived from seeds which have
arisen from cross-pollinated flowers are in many cases taller,
more robust in constitution and productive of earlier flowers and
more seeds than those arising as the result of self-fertilisation.
A great many devices are met with among flowering plants
which are calculated to secure a preponderance of cross-fertilisa-
tion over self-fertilisation. The chief arrangements tending more
or less completely to this end are the following :
(i) The flowers are often diclinous (p. 87); that is, the
sexual organs are produced in separate flowers, which may occur
either on the same plant, as in the hazel and pine, or upon
different individual plants, as in mercury (Mercurialis\ hop and
willow.
(ii) Although the male and female sexual organs in
monoclinous flowers are in close proximity to each other, they
frequently do not ripen together : plants bearing flowers of this
kind are described as dichogamous.
Two types of flowers are met with upon dichogamous plants,
namely, (a) protandrous flowers, or those in which the anthers
ripen and shed their pollen before the stigma is in a suitable
condition to receive it, and (b) protogynous flowers in which the
stigma is receptive some time before the anthers open and set
free their pollen.
Protandrous flowers are abundant ; the sunflower, daisy, dead-
nettle, carrot, bean, vetch, parsley and most Umbelliferae,
Leguminosae, Compositse, and Labiatae are familiar examples : in
these, the pollen necessary for the fertilisation of any particular
flower usually comes from a younger one, because its own pollen
has been shed before the stigma is receptive.
Protogynous flowers are less common : examples are seen in the
apple, pear, plantain (Plantago\ meadow foxtail and sweet vernal-
grasses, rushes, hellebore, and species of Speedwell ( Veronica),
and Calceolaria. In these the stigmas are pollinated from the
TRANSFERENCE OF POLLEN 281
anthers of flowers which have opened previously, their own
anthers being not yet ripe when the stigma is fully developed.
(iii) Among monoclinous flowers which are homogamous y that
is, which develop and ripen their sexual organs simultaneously,
the distance apart or the relative position of the anthers and the
stigma is often Such that the transference of pollen from the
former to the latter is rendered uncertain : examples exhibiting
adaptations of this class are met with in the primrose and cowslip.
(iv) Among certain plants, especially some orchids, the pollen
has no fertilising effect upon ovules produced in the same flower.
Transference of pollen. Since the pollen-grains of plants have
no power of spontaneous movement, they must be carried from
one flower to another by some external agency.
In certain cases snails, birds, and currents of water effect the
transference of pollen from place to place, but the chief agents
which carry the pollen-grains from one flower to another are
(i) the wind and (2) insects.
Flowers which are cross-pollinated by aid of the wind are said
to be anemophilous or wind-pollinated : those in which the pollina-
tion is brought about by the agency of insects are described as
entomophilous or insect-pollinated flowers.
Wind-pollinated flowers are sometimes loosely described as
wind-fertilised and insect-pollinated flowers as insect-fertilised:
it must, however, be clearly understood that the function of
the wind and insects is merely the transference of the pollen-
grains from the anthers of one flower to the stigma of another,
and that these agents have no direct influence upon the act of
fertilisation which subsequently takes place in the ovule.
As examples of plants .whose flowers are wind-pollinated may be
mentioned the hop, docks, almost all grasses and sedges, and many
trees and shrubs, such as hazel and birch. Their flowers are gener-
ally small and inconspicuous, without scent : ' honey ' is generally
absent, and the pollen-grains, which are usually produced in large
quantities, have a smooth and dry external surface. The anthers
20
282 REPRODUCTION
in many cases have long slender filaments which allow of theii
easy movement even by gentle breezes : the stigmas are often
very large and feathery and specially adapted to catch the floating
pollen-grains.
Insect-pollinated flowers, of which roses, honeysuckle, clovei
and primrose may be mentioned as examples, usually have
brightly-coloured petals or sepals, and are often highly-scented,
Nectaries or honey-glands which secrete nectar, a sweet liquic
commonly called 'honey,' occur on various parts of the
flower.
Their pollen-grains are less abundant than in wind-pollinated
flowers and generally have an ornamented sticky surface which
enables them to cling together and to the bodies of insects. The
stigmas of such flowers are comparatively small, and when read]
for pollination often exude a viscous liquid to which the
pollen-grains readily adhere, and in which they germinate
freely.
The insects which visit flowers are mainly beetles, flies
moths, butterflies, and bees. The various tints of flowers
their odour and the nectar which is secreted by them, serve
to attract these visitors, and in certain measure enable the
latter to distinguish the particular species of plant which the]
wish to visit.
Insects feed upon nectar and also to some extent upon pollen
which they obtain in part from wind-pollinated flowers whicl
contain no nectar.
In their search for a livelihood bees and other insects uncon
sciously render useful service to the plants which they visit b]
bringing about cross-pollination.
Where the nectar is exposed or easily accessible, as 5i
most unbelliferous plants and buttercups, a great variety o
insects belonging to different families are attracted, and man]
of them creep about and often merely self-pollinate th<
flowers. In many cases, however, the nectar is secretee
TRANSFERENCE OF POLLEN
283
and stored at the base of long, tubular corollas and calyces,
or in places otherwise difficult of access, where it can only
be reached by insects, such as moths, butterflies, and bees,
possessing long proboscides and tongues, or some particular form
and weight of body. In flowers of this character, the insects
during their search for nectar, touch the anthers, and the
pollen becomes dusted on to their bodies, often at some
particular point, which point is brought into contact with the
71
FIG. 102. i. Flower of white dead-nettle (Lamium
album L). 2 Section of the same ; s stigma ;
a stamens ; r ring of hairs ; n nectary.
stigma of a flower subsequently visited, and cross-pollination is
effected.
An example of the adaptation of a flower to the visits of
large bees may be studied in the common White Dead- Nettle
(Lamium album L.) (Fig. 102). The flower has a conspicuous,
white, two-lipped corolla. The upper lip (u) is arched and
protects the pollen from being washed away by rain ; it also
prevents rain from passing down to the nectary which is present
at the base of the ovary (n). When visiting such a flower, the
284 REPRODUCTION
bee alights on the lower lip (/) of the corolla which acts as a
convenient landing-stage, and pushes its head down the tube
of the corolla in search of the nectar concealed below. The
body of a large bumble bee or a hive bee fits almost exactly
into the mouth of the corolla, and the back becomes dusted with
pollen from the anthers (a) under the upper lip (u). On enter-
ing another flower, the back of the bee with the pollen upon
it comes first into contact with the lower half of the bifid
stigma (s) which projects a short distance below the anthers,
and cross-pollination is readily effected. Pollen from this
second flower is removed on leaving and transferred to a
third, and so on. The tongues of flies and other insects
whose bodies are not stout enough to fill up the mouth of the
corolla, and come in contact with the anthers, are too short to
reach the honey ; moreover, a ring of hairs (r) arranged across
the lower part of the corolla tube prevents small insects from
robbing the flower of its nectar. Almost all zygomorphic flowers,
such as the bean, clover, sainfoin, mint, snapdragon, and many
others, exhibit striking adaptations to secure cross- pollination
by the agency of insects, and many of these, when insects
are prevented from visiting them, are practically unable to
effect self-fertilisation, and hence produce little or no seed
under such circumstances.
It must, however, be mentioned that although many flowers,
such as those of the broad-bean, broom, carnation, red clover
and foxglove, are either unable to produce seed, or produce but
few, when insects are excluded, others which show special adapta-
tion for cross-pollination by insects, and which are usually and
most advantageously pollinated by these agents, have also the
power of self-fertilisation, and often exercise it in dull weather,
or at other times when insect-visitors are scarce. For example,
the flowers of vetch, pea, dwarf-bean (Phaseolus vulgaris) and
tobacco produce seeds when specially protected from being
cross-pollinated by insects. Many protogynous flowers in a
SEXUAL AFFINITY 285
young state are adapted for cross-pollination, but if the latter
does not take place, the stigma frequently receives pollen from
its adjoining anthers at a later stage of development of the
flower.
Ex. 170. Examine the following wind-pollinated flowers: grasses, sedges,
rushes, oak, walnut, birch, alder, hazel, hop, plantain and dock.
Note (i) the absence of conspicuous calyx or corolla.
(2) Powdery, dry, character of the pollen.
(3) The extensive receptive surface of the stigmas.
(4) General absence of scent and nectar.
Ex. 171. Examine the following insect-pollinated flowers: buttercup,
columbine, monk's-hood, poppy, cabbage, pansy, violet, pink, carnation,
primrose, stitchworts, mallows, horse-chestnut, bean, clovers, birds' foot
trefoil and other leguminous plants, strawberry, apple, pear, cherry, plum,
dandelion, sunflower, thistle, knapweed, parsnip, carrot and other un-
belliferous plants.
Make an examination of the flowers in different states of development, and
note :
(1) Whether they are protogynous or protandrous.
(2) Where the nectar is secreted and stored if any is present : it may be at
the base of the stamens, on the receptacle, ovary, or in specially constructed
parts of the petals and sepals. Frequently ridges and variegated stripes of
colour on the petals point in the direction of the nectary, and apparently
serve as guides to insect-visitors.
(3) Determine whether there is any specially convenient landing-place for
insect-visitors, and try and find out whether the stigma or anthers are touched
first when insects visit the flowers.
(4) Whenever opportunity offers, carefully watch insects at work extract-
ing honey or collecting pollen from flowers.
7. Sexual affinity : hybridisation and hybrids. A fertile
sexual union between the male cell of a pollen-grain and
the egg-cell within an ovule does not take place indiscrimin-
ately among plants. A certain relationship or sexual affinity
must exist between the parent plants before their reproductive
cells will unite.
Although self-fertilisation is possible, and among certain plants
is a normal process, experience teaches that in many cases
286 REPRODUCTION
the pollen of a flower has no fertilising effect on the egg-cells
of ovules present in the same flower or in flowers on the same
individual plant.
Moreover, it is generally found that fertilisation between the
reproductive cells of plants widely different from each other, say,
between those of a cabbage and a potato, or those of a peach
and a turnip, does not take place.
In some instances the cause of the failure of the pollen
of one plant to fertilise the ovules of another may possibly
be due to the want of power of the pollen-grain to develop
pollen-tubes long enough to reach from the stigma to the
ovules within the ovary ; or the tissues of the style may offer
some mechanical obstruction to the advancing pollen-tubes.
In most cases, however, it would appear that there is
some other quite unknown cause at work which prevents
the living substance, composing the reproductive cells of
certain plants, from exercising a fertilising influence on each
other.
When the relationship between the male and female repro-
ductive cells is too close, and also when it is too remote, fertility
is reduced. For the production of the most vigorous and the
most prolific progeny there must be a certain degree of difference
between the productive cells which unite.
As pointed out previously (p. 279) the most fertile sexual
union takes place between the reproductive cells of flowers
which arise on different individual plants of the same species.
The progeny resulting from such cross-fertilisation grow
luxuriantly and produce numbers of seeds capable of giving
rise to equally robust offspring.
It is also found that well-marked, wild and cultivated varieties
and races of the same species of plant generally cross readily :
thus, the cross-pollination of different varieties of wheat, barley,
turnips, apples, carnations, roses and other plants, results in the
production of ^flfcoring. The progeny arising from cross-fertilisa-
SEXUAL AFFINITY 287
tion between two varieties or races of the same species are termed
cross-breeds, or variety-hybrids.
Variety-hybrids usually possess the following characters :
(i) They are often more luxuriant and robust in constitution
than their parents ; their roots are frequently extensive and the
shoots and leaves large.
(ii) They usually grow more rapidly, flower earlier, and
produce a larger number of flowers than the parents.
(iii) The power of seed-production is strong and their seedling
offspring is generally very vigorous.
It has been found in a large number of instances that the
pollen of one plant cannot impregnate the ovules of another
widely differing from it, but we have no means of determining
beforehand whether any two particular species will cross suc-
cessfully ; nothing save actual trial will decide.
Many examples are known where cross-fertilisation does take
place between different species of plants, as for example, between
the raspberry and blackberry, wheat and rye, different species
of strawberry (Fragaria) and various species of Pelargonium,
Dianthus, Narcissus, Digitalis, Viola, Gladiolus, Begonia and
many other ornamental flowering - plants. Cross - fertilisation
between distinct species of plants is termed hybridisation, and
the progeny of such crossing are termed hybrids-, when the
species crossed belong to the same genus, the progeny are some-
times designated species-hybrids, to distinguish them from genus-
hybrids, or bigeneric hybrids the progeny of species belonging to
different genera.
Few or no crosses are known with certainty between plants
belonging to different Families or Orders ; even genus-hybrids
are comparatively rare.
Generally the more nearly allied the species are the more
readily do they hybridise. .
The species belonging to certain Orders seern naturally in-
clined to hybridisation ; especially is this true of the Composite,
288 REPRODUCTION
Orchidaceae, Iridaceae and Scrophulariaceae : on the other hand,
among the Cruciferae, Leguminosae and Umbelliferae hybrids are
uncommon.
True hybrids or crosses between distinct species of plants
usually exhibit the following characters :
(i) If the parents are very widely different from each other,
the offspring is usually delicate and difficult to rear, but where
the parents are more nearly related the offspring is frequently
taller and more vigorous and luxuriant in its vegetative organs
than either of the parents.
(ii) In nearly all cases hybrids are less fertile than their
parents: their sexual organs are weak, and frequently they are
absolutely sterile, the anthers producing no pollen or the
carpels no ovules, so that seed-formation is impossible. In
certain rare instances there appears no inclination or power
to form flowers. In those which do produce flowers and
seeds the pollen-grains are generally smaller in size and
number, and the ovules more or less imperfectly formed : the
male reproductive organs are more deleteriously affected than
the female organs.
(iii) The petals and coloured parts of the flower are generally
larger and more lasting than those of either parent. ' Doubling '
of the flowers and other pathological malformations are more
common among hybrids.
(iv) In the first generation raised from seeds obtained by
cross-pollinating distinct species, all the individual plants are, in
most instances, similar to each other, but the degree of
resemblance to the two parents varies considerably.
The individuals of the second or later generations, that is,
the offspring which arise from self-pollination or cross-pollination
of the flowers of hybrids, vary much in form and in other ways :
they do not resemble each other nearly so much as those of
the first generation. Some of them almost exactly resemble
the female, others the male parent, while many show the
MENDELIAN LAWS OF INHERITANCE 289
characters of both parents combined in various degrees. More-
over, in many instances, entirely new characters, not seen in
either parent, arise among the offspring of succeeding generations
of hybrids.
(v) Hybridisation is usually, though not always, reciprocal :
if the pollen of a species A is effective upon the ovules of
another species B, the pollen of B is usually similarly effective
upon the ovules of A.
In most instances there is no difference between the offspring
of reciprocal crosses.
It has been noticed also that in the crossing of certain species
the hybrids produced always resemble one of the species more
than the other, no matter whether it is used as the male or the
female parent of the cross.
Almost all hybrids are more easily crossed with pollen derived
from one of the parent species than with pollen from its own
flowers or from flowers of another hybrid of the same origin as
itself : the progeny of such crossing are termed derivative hybrids.
Most derivative hybrids are intermediate between the parent
and the original hybrid : they are more fruitful than the
latter, and some of them frequently come true from seed.
If such hybrids are again pollinated by the same parent,
the progeny or members of the third generation resemble the
pollinating parent more closely ; by a repetition of the crossing
with the same parent up to the fourth or fifth generation, all
trace of the original second parent of the hybrid is lost or un-
recognisable in the progeny.
True hybrids may be crossed with another species different
from either of the parents, and the offspring, which may be
termed trispecific hybrids^ can be crossed again with still another
distinct species. In this manner plants have been obtained
combining the characters of three, four, or more species : the
offspring of such crossed plants are very variable.
8. Mendelian laws of inheritance. (i) Since 1900 much
2pO REPRODUCTION
attention has been devoted to experimental work upon the
character of hybrids, or crosses between varieties of plants, and
those exhibited by their offspring.
Some remarkable facts were observed by Gregor Johann
Mendel in Germany about 1866, but the published accounts of
his work and the ' laws of inheritance ' deduced from it were lost
sight of until about 1900, when De Vries in Holland, Correns in
Germany, and Tschermak in Austria rediscovered similar facts.
Mendel worked chiefly with garden peas, and crossed certain
varieties which differed from each other in regard to some
simple character or pair of characters.
Among other experiments he crossed a variety of pea having
smooth round seeds with one bearing wrinkled indented seeds,
and found that the offspring consisted invariably of plants which
bore only smooth round seeds : the wrinkled character of the
parent crossed was not seen in the hybrid obtained.
That character of the parent which appeared in the offspring
of the first cross he termed dominant^ the character not seen
being spoken of as recessive.
Seeds arising from the self-fertilisation of the flowers of the
round-seeded hybrid gave rise not only to round-seeded peas
but to plants with wrinkled seeds as well
The number of seeds showing the dominant round character
was found to be three times as many as those exhibiting the
recessive wrinkled character.
Mendel continued the raising of plants from these seeds
through several generations, and found that the wrinkled seeds
bred true : they were as pure in respect of the recessive
character as the original parent, and never gave rise to round
peas.
The round seeds, however, behaved differently. One in every
three bred true ; it was pure in regard to the dominant character,
but two of the round seeds in every three gave offspring which
MENDELIAN LAWS OF INHERITANCE 291
bore both round and wrinkled seeds. They were hybrid like
the first cross, and the proportion of round seeds to wrinkled
ones which they produced was 3 to i .
If we assume that each plant produces say 4 seeds, the
following scheme indicates the proportion of each kind obtained
in three successive generations ;
Parent Parent
R x W
round crossed with wrinkled
gives rise to
RW 1st hybrid
4 round (impure) generation
dominants
From these
are obtained
(termed the
F! generation)
(F, generation)
-^~
12 round
(dominant)
+
7"
4 wrinkled
(recessive)
4 pure
(W)
4 pure
(R)
+
8 impure
(RW)
I
16 round 24 round + 8 wrinkled 16 wrinkled (F, generation)
(all pure \ / 8 pure + 16 impure \ /all pure\ /all pure \
R H * RW )( W )( W )
(ii) That certain characters of plants are dominant over
others when crossing takes place was well known before
Mendel's time, and that among the later generation or off-
spring of crosses, individuals bearing the parental character
not seen in the first generation are obtained, was also known,
but the average numerical proportion of each was not noticed
previously.
The most important feature of Mendel's work, however, lies
in the explanation which he offered of the facts.
He propounded the hypothesis that, so far as a pair of char-
292 REPRODUCTION
acters which exclude each other or are opposed to each other are
concerned, each male or female reproductive cell or gamete of the
hybrid carries only one of the characters, not both. It is assumed
that in each gamete there exists something which induces or
controls the appearance of a character in the offspring of a plant :
this is termed & factor or gene. Thus, there are factors or genes for
height of plant and for shape of seed in- the gametes of peas.
There is considerable evidence that the genes are carried in the
chromosomes of the nuclei of the gametes.
Although the hybrid plant arising from the union of reproduc-
tive cells of, say, a pea, with round seeds, and one bearing wrinkled
seeds, contains both of these characters, even if both are not
visible, its reproductive cells carry only the round or the wrinkled
character in a pure state; its pollen-grains and ovules or the
generative nuclei in them, are either pure ' round ' or pure
* wrinkled/
Moreover, Mendel assumed that the number of male cells (ancf
female cells) bearing the ' round ' character was on an average
equal to those carrying the ' wrinkled ' character.
Such assumptions being made, the result of the union when only
self-fertilisation is allowed will be understood from the following :
A hybrid plant produced by the crossing of a parent bearing
round seeds (R) with one bearing wrinkled seeds (W) possesses :
Male Gametes. Female Gametes.
Some bearing the character R ^^ ^ R
Any male gamete bearing the R (round) character has an
equal chance of meeting with a female gamete carrying R or W.
If it meets with R the plant produced will bear round seeds, and
will be quite pure (RR) in respect of this character of round-
MENDELIAN LAWS OF INHERITANCE 293
ness. If it meet with a gamete bearing W, the resulting plant
will be hybrid, and will not breed true,
We thus see that on an average there will be formed from
the male gametes carrying the round character, uniting at
random with the female gametes available
T>T i
pure RR plants
-, -DT X r r proportion to
nd RW P
^ i
jhyb
Similarly, from the male gametes possessing the wrinkled
character (W) we should have
(pure WW plants) in the ' WW
1u u :A T>\\T I proportion ^
^hybrid RW J f
Taking the combination of all the gametes at random, where
the number of male and female sex cells each bearing only one
(R or W) of two characters is the same, we should have the
following proportional result :
i plant 2 plants i plant
RR RW W\V
Dominant. Recessive.
As the round is dominant over the wrinkled character, the
impure hybrid plants (RW) will look like the pure (RR) plants.
Therefore the proportion of plants showing the round dominant
to those exhibiting the recessive wrinkled character would be
3 to i, which is what Mendel found to be actually the case in
his experiments.
294
REPRODUCTION
When the hybrid was crossed with the parent bearing the
wrinkled character, instead of being self-fertilised, the off-
spring consisted of round and wrinkled peas in equal pro-
portion, which is also what would be expected from Mendel's
hypothesis.
Gametes of
Hybrid.
R
Gametes of
Parent.
RW
WW
RW
WW
i RW
to
i WW
(iii) Characters which exclude or contrast with each other, as
the ' roundness ' and * wrinkledness ' of peas, are spoken of as a
pair of allelomorphs.
A plant or animal which arises from the union of two distinct
germ-cells is sometimes termed a zygote.
The individual plant formed from the fertilisation of sexual
cells bearing similar allelomorphs is termed a homozygote (RR for
example). Where the allelomorphs are antagonistic the resulting
plant is spoken of as a heterozygote (as RW).
(iv) The following have been found by experiment to behave
as allelomorphic pairs of characters :
In
Peas
Wheat
Lychnis
Chelidonium
Maize
(Enothera
Sweetpea
Many plants
majus
Dominant.
Tall habit
Yellow cptyledon
Brown skin
Round seeds
Absence of awns
Rough chaff
Red chaff
Hairiness
Entire petals
Starchy endosperm
Long style
Oval pollen-grains
Coloured flowers
Recessive.
Dwarf habit
Green cotyledon
White skin
Wrinkled seeds
Presence of awns
Smooth chaff
White chaff
Smoothness
Laciniate petals
Sugary endosperm
Short style
Round pollen-grains
White flowers
MENDELIAN LAWS OF INHERITANCE 295
(v) Mendel crossed peas varying in several characters and
obtained results similar to those found in crossing plants with
round and wrinkled seeds described above. For example, crosses
between tall and dwarf varieties give seeds from which are grown
the first (Fj) generation of hybrid plants, all of which have tall
stems, * tallness ' being a dominant factor. Segregation or split-
ting into tall and dwarf plants, in the proportion of 3 tall : i
dwarf, takes place in the second (F 2 ) generation, but it is not until
the plants of this generation attain their full development that
their characters in respect of height can be determined.
Similarly, in the cross between a plant with coloured flowers
in which the colour factor for colour is dominant and one with
white flowers, the flowers of the first (F x ) generation are usually
all coloured. Segregation also occurs in this, as in the other cases,
among the plants of the second (F 2 ) generation, but, of course, it
is again not until they are fully developed that both coloured and
white flowers are seen.
One of the classic examples of the crossing of peas by Mendel
was made between plants with yellow seeds and those with green
seeds. The peculiar tint of the seeds of these peas is due to the
colour of the cotyledons of the embryo plants within the seeds,
which colour is visible through the translucent seed coats.
In the cross mentioned, yellow is the dominant factor, and the
seeds in the pods of the cross are all yellow. These seeds, when
sown, give rise to the first (Fj) generation which bear yellow and
green seeds, often both kinds in the same pod, in the proportion
of 3 yellow : i green.
To one who repeats this experiment for the first time the result
is somewhat puzzling, for he does not expect to meet with both
yellow and green seeds until ripe pods are developed on the full-
grown plants of the second (F 2 ) generation : that they are found
in pods of plants of the first (F x ) generation is surprising.
The difficulty, however, is removed if it is realised that the
two kinds of plants segregated in the second (F 2 ) generation are
296 REPRODUCTION
present as embryos, with cotyledons of their respective colours in
the seeds borne on plants of the first (F x ) generation ; it is there-
fore not necessary to raise full-grown plants of the second (F 2 )
generation in order to observe the characters whose transmission
from generation to generation is being studied, as it would be if
the hereditary transmission of flower colour or height of plants
were being investigated.
In the examples previously given of the crossing of two varieties
of pea, each differing from the other in respect of ' roundness '
and ' wrinkledness ' of their seeds, or yellow and green colour of
their cotyledons, the homozygous and heterozygous dominants
are indistinguishable ; the recessive is completely hidden by the
dominant character in the first, or F x generation : its presence in
the hybrid is unsuspected although its existence is immediately
revealed in the progeny of the F 2 generation.
Such complete dominance is, however, not an invariable rule,
for all the individuals of a cross between a tall and a dwarf variety
of a plant are frequently intermediate in height, being shorter than
the tall and taller than the dwarf parent.
Similarly, in a cross between two varieties of the same species
of plant, one with deep rose, the other with white flowers, all the
individuals of the F x generation bear pale pink flowers : self-
fertilisation of the latter gives in the F 2 generation, progeny of
three types, namely, plants with rose, pink and white flowers
respectively, in the ratio :
12 I
rose pink white
like one like the like the
grandparent hybrid parent other grandparent ;
typical Mendelian segregation, the only unusual feature being the
flower colour of the heterozygous individuals, which differs from
that of the homozygous dominants.
The character of the segregation is clear, if it is assumed that
MENDELIAN LAWS OF INHERITANCE 297
the rose parent is a homozygous rose plant, RR, having a double
dose of the R factor for rose, the hybrid being heterozygous, RW,
with only one dose of R.
Thus :
Rose Parent. White Parent.
RR WW
Gametes.
RW pink hybrid.
Male Gametes of the hybrid.
R, W
Female Gametes of the hybrid.
R, W
A male gamete, R, has an equal chance of mating with either
an R or W female gamete ; and likewise the other male gamete,
W, has an equal chance of fusing with an R or W female gamete.
The possible combinations are given in the diagram below ;
Male Gametes of the hybrid.
Female R W
Gametes. __
R
W
or, i RR
rose
RR
RW
i WW
white
RW
WW
. : 2 RW :
pink
As already noted, self-fertilisation, or inbreeding, oi netero-
zygotes leads to segregation of the parental types in the offspring.
A true-breeding race exhibiting only the special characters of the
heterozygote cannot, therefore, be obtained, and attempts to
'fix' such plants is doomed to failure; these special characters
are not represented in the gametes of the hybrid, their appearance
there being due to the meeting of dissimilar gametes.
Among other examples of heterozygous * unfixable ' characters,
21
REPRODUCTION
are (i) the commercial carnation with * double ' flowers and non-
bursting calyces, the product of the crossing of plants with ' single '
flowers and plants with excessively ' double ' flowers whose crowded
petals split the calyces along one side ; (2) Blue Andalusian fowls,
the particular tint of which appears when black and white varieties
of the breed are crossed ; (3) the roan colour of Shorthorn cattle
obtained when white and red animals are crossed.
Many other examples might be mentioned of imperfect dominance,
in which the heterozygote differs from the homozygous dominant.
(vi) After dealing with peas varying in one pair of characters,
Mendel crossed varieties exhibiting two pairs of allelomorphs
and determined the distribution of the parental features among
the offspring.
When a pea plant having tall stems and round seeds is crossed
with a plant with dwarf stems and wrinkled seeds, two allemorphic
pairs are involved, viz., (i) ' tall ' and ' dwarf ' ; (2) ' round ' and
1 wrinkled/
(1) * Tall ' stems are dominant to ' dwarf ' stems.
(2) ' Round ' seeds are dominant to ' wrinkled ' seeds.
All the plants from the first cross, or the F x generation, are
found to be tall plants with round seeds.
On self-fertilisation the F 2 generation is obtained. This yields
four types of plants, namely :
1. Tall plants with round seeds 3. Dwarf plants with round seeds
2. wrinkled 4. wrinkled
in the following proportion :
9 : 3 : 3 ' i
tall, round tall, wrinkled dwarf, round dwarf, wrinkled
Two of these types are like the original parents in appearance,
but in addition to these, two new varieties have been obtained,
namely, tall plants with wrinkled seeds and dwarf plants with
round seeds.
MENDELIAN LAWS OF INHERITANCE 2976
On Mendel's hypothesis, this result, both as regards the height
of the plants and shape of the seeds, as well as the proportion
of each, is to be expected, as appears from the diagram below
Parent. Parent.
TR X DW
TRDW F! generation,
a tall plant bearing round seeds, since ' tall ' and * round ' are
dominant to ' dwarf ' and ' wrinkled ' characters respectively.
The gametes of the hybrid would be
Male. Female.
TR TR
TW TW
DR DR
DW DW
The TR male gametes have an equal chance of mating with
either TR, TW, DR or DW female gametes.
Similarly TW do. do. do. do.
DR do. do. do. do.
DW do. do. do. do.
The possible combinations are seen in the following diagram.
Male Gametes.
Female TR TW DR DW '
Uametes.
TR
TW
DR
DW
TR X
TR
TW X
TR
DR X
TR
DWj
TR
TR t
TW
TW 2
TW
DR t
TW
DW a
TW
TRj
DR
TWi
DR
DR 3
DR 3
DW 3
DR
TR,
DW
TW 2
DW
DR 3
DW
DW 4
DW
REPRODUCTION
a. Those marked (i) in which TR occurs will all be alike in
appearance, viz., tall plants with round seeds, * tall ' and * round '
being dominant characters. Of these there are nine.
b. Three marked (2), TW TW, DW TW, TW DW, are tall
plants with wrinkled seeds ; R is absent.
c. Three marked (3), DR DR, DW DR, DR DW, are dwarf
plants with round seeds. T is absent and R is dominant.
d. One marked (4), DW DW, is a dwarf plant with wrinkled seeds.
One of the nine tall plants with round seeds, namely, TR TR,
is exactly like one of the original parents of the cross and will
breed true, the single dwarf plant with wrinkled seeds, DW DW,
being the true-breeding segregate like the other parent.
One of the three plants with tall stems and wrinkled seeds,
TW TW, a new combination, will breed true.
One of the three dwarf plants with round seeds, DR DR, also
a new combination, will breed true.
The remainder of the plants obtained are impure or hybrid' in
respect of one or other allemorphic pair of characters and con-
sequently will not breed true, but will segregate in various ways
when self-fertilised.
From the above example it is seen that certain characters
existing in two separate varieties of plants may be combined in
one variety, and this is not an isolated case. Many others have
been worked out experimentally.
(vii) In some cases the independent factors of an allelomorphic
pair interact with each other, leading to complicated examples of
inheritance, which at first sight seem to contravene Mendelian
laws.
A remarkable example of such has been observed in the cross-
ing of certain varieties of Sweet Peas. Two different pure white-
flowered varieties are known, each of which breeds true to the
white colour ; these when crossed give rise in the first (F x ) genera-
tion to plants with purple flowers closely resembling those of the
Wild Sweet Pea, from which all the garden varieties have been
MENDELIAN LAWS OF INHERITANCE 297**
derived. In the second (F 2 ) generation both white and purple
flowered plants are obtained in the proportion of 9 purple : 7
white, numbers which suggest the Mendelian ratio of 9:3:3:1
observed in the progeny of the hybrid between a tall, round
seeded and a dwarf, wrinkled seeded plant just described, and
in many other crosses between varieties of plants differing in two
pairs of allelomorphic characters.
It would appear that the purple colour is the result of the
coming together of two independent dominant factors, the absence
of one or both of which in the zygote gives a white-flowered
plant.
Representing one of these factors by X, the other by Y, and
their absence by x and y respectively, one white parent may be
denoted by XXyy, the other by YYxx.
Gametes of the two white parents.
Xy Yx
Xy Yx F x hybrid
The gametes formed by the F x hybrid are XY, Xy, xY, xy ;
their possible combinations are indicated in the following diagram.
Female
Gametes.
XY
Xy
xY
Male Gametes.
XY Xy xY xy
XY 1
Xy,
XY
xy
&
Xy 1
Xy a
Xy
Xy
$
xY 1
xY 1
xY.
xY 3
xY 3
xy
Xy,
xy
xY 8
xy
xy
298 REPRODUCTION
Nine marked (i) contain both X and Y, and are therefore
purple flowered. In the three marked (2) Y is absent ; in the
three marked (3) X is missing \ while in (4) both X and Y are
wanting ; all these are therefore white-flowered.
The ratio is 9 : 3:3:1
purple white
(viii) The Mendelian conception of distinct unit characters
which are capable of being inherited independently of each other
has given precision to our views of the nature of heredity and the
constitution of pure breeds and hybrids or crosses.
A pure-bred individual is one which has developed from the
union of male and female cells containing similar elements or
characters, while a hybrid or cross-bred organism has arisen from
sex cells conveying different allelomorphic elements. A plant
may be pure bred in respect of one character and yet be cross-
bred in regard to another character.
This hypothesis of the distinctness of hereditary characters
greatly assists the efforts of the plant breeder, inasmuch as it
indicates the line along which crossing must take place to effect
a desired combination in one plant of characters only met with
in separate varieties, and makes his selection among the offspring
of crosses to obtain the wished-for result simpler and more direct
than heretofore.
(ix) It has been long known among hybridists that certain
cross-bred varieties of plants which exhibit characters different
from either of the two parents cannot be fixed. On self-fertilisa-
tion the new character is not met with in all the offspring, there
being many individuals (rogues) which have to be discarded.
No amount of selection or self-fertilisation is found to fix the
new type.
These hybrid forms are generally merely heterozygotes, and
on Mendel's hypothesis ought to break up into 25 per cent.
ARTIFICIAL POLLINATION
like each parent, with 50 per cent, hybrid again, which they
generally do.
Mendelism, moreover, throws considerable light on various
forms of * reversion ' (p. 318).
Some " ' reverted ' individuals which appear among what is
thought to be a selected so-called pure stock, are merely
recessives which have never had the chance of showing them-
selves. The majority of the selected stock might be pure in
MendeFs sense yet if some were impure and contained the
recessive character the latter would only be seen when crossing
took place between individuals possessing the same recessive
character, and the chances in favour of this occurrence might
be very remote on account of the numbers of pure population
among which the impure individuals were mixed.
Such * reverted' individuals ought to breed true when
crossed among themselves or self-fertilised, and this is sometimes
the case.
There are other * reversions ' which do not breed true among
themselves in the first (Fj) generation, yet show a small
percentage which breed true to the reversionary character in the
second (F 2 ) generation, and cannot therefore be of heterozygote
nature.
Such cases are seen in what is termed Reversion on
crossing/
These can also be explained on Mendelian lines, but further
information regarding them must be sought in works specially
concerned with the subject.
9. Artificial pollination : methods of crossing plants. Several
plants, such as the melon, peach, tomato and egg-plant, which do
not set fruit unless the ovules are fertilised, must be cross-
pollinated artificially when grown under glass and forced to
bloom in early spring or at other seasons of the year, when
pollinating insects are not abundant,
300 REPRODUCTION
The process consists merely in a transference of pollen to the
stigmas of the flowers by means of a camel's-hair brush, a plume
of pampas-grass, or a rabbit's tail fastened to a small stick.
In the case of the tomato, peach, and other plants with mono-
clinous flowers, merely shaking the plants is sometimes sufficient
to distribute the pollen satisfactorily, but the most efficient
method in the case of the peach and melon is first to collect
the pollen from the anthers by means of a camel's-hair brush,
and then apply the pollen-laden brush to the stigmas of the
flowers : with tomatoes it is best to shake a quantity of pollen
from several flowers into a watch glass or spoon, and then dip
the stigmas of the flowers into the pollen so collected.
In the case of the melon where the flowers are diclinous,
the staminate flowers are sometimes pulled off the plant, and
after rolling back the corolla, the exposed anthers may be gently
brushed over the stigmas of the pistillate flowers intended to be
pollinated, or a whole male flower may be pushed into the corolla
of one of the latter and left there. Of course, in these and all
other instances the anthers must be in a dehiscent condition, so
that the pollen-grains are fully formed and easily set free, and
the stigmas must be in a receptive condition.
Where it is desired to cross or hybridise two particular varieties
or species of plants, it is necessary to proceed in a more careful
manner. One or more flowers upon the plant which is to act as
the female parent or seed-bearer, must be selected for the opera-
tion, and must be prevented from receiving any other kind of
pollen upon their stigmas except that from a flower from the
plant which has been chosen as the male parent.
Before attempting to cross two plants it is important to study
and become familiar with the structure of their flowers in regard
to the number and position of their sexual organs and whether
the flowers are protandrous or protogynous ; moreover, a know-
ledge of the appearance presented by the stigmas when they are
ARTIFICIAL POLLINATION 301
ready to receive pollen, and the mode and time of dehiscence of
the anthers when the pollen is mature, is useful.
The receptive surfaces of the stigmas of flowers when mature
are often moist or sticky : in other cases they enlarge and appear
rough and covered with very small round prominences when
viewed with a lens. Where the stigmas are bifid the two halves,
which in an immature state lie close together, separate and curl
away from each other when mature.
The details of the actual method of cross-pollination varies
with the structure and arrangement of the flowers to be operated
upon, and also to some extent upon the taste and fancy of
the operator. The following plan gives excellent and accurate
results :
(i) First select the flower to be used as the seed-bearer. This
must be done before the flower has opened and before its own
anthers are mature enough to shed their pollen. Unless this
precaution is adopted self-pollination or cross- pollination by
agency of the wind or insects may have already taken place.
Where several flowers are borne somewhat close together as
in the apple and wheat, one or two only should be crossed and
the others removed, so that the crossed specimens may have a
better chance of developing.
(ii) Open the flower and carefully remove the stamens with
fine-pointed forceps taking hold of each stamen by its filament
so as not to crush the anther and thereby run the risk of setting
free the pollen.
Where the stamens are epipetalous and in other instances it
is sometimes more convenient to cut off the calyx, corolla, and
stamens with fine scissors. Be careful not to touch or injure
the style and stigma of the gynaecium.
After this process of emasculation or removal of the male
sexual organs, the flower or the shoot bearing it must be
enclosed in a paper bag tied up at the mouth so as to exclude
302 REPRODUCTION
insects and prevent wind-pollination : allow the stigma to mature,
which usually takes two or three days according to the age of
the flower when emasculated.
(iii) When the stigma is ready, remove some ripe stamens
from the flowers of the plant to be used as the male parent of
the cross, and after lightly crushing the anther on the finger-
nail so as to set free the pollen, transfer the latter by means of
forceps to the stigma. To ensure absolute accuracy the flowers
from which the pollen is taken should have been previously
enclosed in a paper bag and allowed to open there: if this
precaution is neglected and stamens are merely taken casually
from open flowers on the male parent there is no certainty about
the cross for foreign pollen may have been brought into contact
with them by the wind or by insects.
(iv) After pollination has been effected the flower must be
again enclosed in a paper bag and kept there until the seeds
have been fertilised and the fruit has begun to grow.
The bag may then be removed and the fruit and seeds allowed
to ripen in the ordinary way ; in the case of fruits, such as apple,
pear and raspberry, it is necessary to protect the ripening fruit by
means of a muslin bag or coarse net.
CHAPTER XXIII.
CULTIVATED PLANTS AND THEIR ORIGIN:
PLANT BREEDING.
i. FROM the most remote ages the human race has derived
much of its sustenance from the Vegetable Kingdom. At first,
no doubt, men were content to roam about and feed upon the
roots, stems, leaves, fruits and seeds of various species of plants
found growing wild, just as the lowest savage races do at the
present day. With a settled mode of life and increasing
population would come the necessity to select and cultivate
close at hand particular species possessing useful and agreeable
qualities, so that a constant and more certain supply of food
might always be obtained.
By whom or at what period in the history of mankind was
begun the selection and first cultivation of the different wild
plants which have given rise to our chief cultivated food-plants,
is not known. Extensive researches by De Candolle and others
have shown that the majority of our common vegetables, fruits and
cereals have been in cultivation for many hundreds and in some
instances thousands of years : during this time they have under-
gone extensive modification.
In the case of common bread wheat, maize, broad bean, and a
few others, the wild species from which they have been developed
are unknown ; in most cases, however, the wild prototype of the
various cultivated farm and garden plants can be recognised with
more or less certainty. On comparing cultivated varieties with
the wild species it is noticed that the former differ from the latter
in possessing a greater development and generally an improved
80S
304 CULTIVATED PLANTS AND THEIR ORIGIN
flavour of those parts of the plants, for which they are grown,
the other parts or members of the plant being much the same
in both the wild and the cultivated state.
For example, among apples, pears, plums, strawberries and
other plants which are grown for their fruits, the flowers, stems
and leaves are similar to those of the crab, wild pear, sloe and
strawberry from which they have been derived, but how different
are their fruits.
In the cases of plants grown for their roots only, it is the root
which manifests the greatest amount of deviation from the wild
prototype, as may be seen by comparing the roots, stems, leaves
and flowers of the wild carrot and wild parsnip with those of the
cultivated varieties.
The peculiar characteristics which distinguish cultivated from
wild plants are seen to be connected with increased usefulness
to mankind, and it is through man's agency that these useful
modifications have reached their present state of development :
without the care and constant attention of the farmer and
gardener the cultivated types would disappear.
In addition to the maintenance of cultivated varieties at their
present level of excellence endeavours are continually being
made to modify and improve them ; old varieties are being
altered so that either the yield of their useful parts is increased,
or the colour, size, form, flavour, time of ripening, keeping
qualities or hardiness are improved. The mode in which this
improvement takes place is indicated in the subsequent paragraphs
of this chapter.
2. Bud-varieties or ' sports/ The buds upon a plant resemble
each other so much that they all develop into shoots very closely
alike, so far as the colour and form of their stems, leaves,
flowers and fruits are concerned. It is, however, occasionally
noticed among perennial farm and garden plants that single buds
upon certain individuals grow out and produce shoots which
differ very greatly from the shoots arising from the rest of the
'SEMINAL SPORTS' 305
buds upon the plant. Thus, single buds upon peach trees have
been observed to develop into shoots which, instead of bearing
peaches, bear nectarines, and plum trees ordinarily producing
purple fruit have been known to give rise to a single shoot
bearing yellow plums of a totally different character from any
previously known.
Such sudden and extensive variation is termed bud-variation
or 'sporting,' and is most frequently met with in those species of
perennial plants which have been under cultivation for very long
periods of time. It is extremely rare among annual plants and
is also uncommon among perennials which have only recently
been introduced into the garden.
Very few c sports ' can be propagated by seeds ; they must
consequently be removed from the parent and multiplied vege-
tatively, that is, by cuttings and layers or by budding and grafting.
Many examples of new varieties of plants which have originated
from bud-variation are met with among garden flowers such as
roses, carnations, chrysanthemums, tulips and pelargoniums.
Also in this manner have arisen practically all the variegated-
leaved and * weeping* forms of ash, willow, box, holly, and
other trees and shrubs.
Among farm crops potatoes are subject to bud-variation, but
its occurrence is extremely rare : varieties bearing tubers with
purple skins have, however, been known to produce single white
tubers among those of ordinary colour, and purple-skinned tubers
have been observed with one or more white * eyes ' which, on
being cut out and propagated, have grown into plants bearing
white-skinned tubers only.
3. Variation among seedling plants.
(a) ' Seminal sports ' : selection and fixation of varieties.
One of the most important peculiarities of living things of all
kinds is the variability of their sexually-produced offspring.
Although bean seeds always produce bean plants and wheat
grains invariably give rise to wheat plants, nevertheless no two
306 CULTIVATED PLANTS AND THEIR ORIGIN
seedlings of these or any other species are exactly alike in all
respects. The variation may be merely morphological, that is,
it may consist in an alteration in the form and size of the leaf,
stem, or other part of the plant : the individuals may also differ
physiologically from their parents and from each other; for
example, among potatoes the seedlings differ in their power of
starch formation and storage, and in their capability of resisting
frost and the attacks of irwects and parasitic fungi.
The differences between the parents and their offspring in the
case of wild plants are usually slight, but among a number of
cultivated plants the amount of variation seen in the seedlings
is often very considerable.
A seedling which differs appreciably from its parent in some
of its morphological or physiological characteristics may be termed
a ' seminal sport?
In some instances the peculiar variations are of the nature of
permanent modifications and transmitted to the offspring of
succeeding generations ; such variations are termed mutations, in
contradistinction to fluctuations or transient modifications, which
are not hereditary.
Although many * seminal sports' differ considerably from
the parent stock from which they have been obtained, it does
not follow that these varieties are necessarily improvements upon
the parents; the majority are often mere curiosities, or distinctly
inferior varieties, with no intrinsic value from the farmer's or
gardener's point of view; others, however, frequently possess
characters of sufficient novelty and distinctness to render them
especially worthy of cultivation.
The latter is perhaps most commonly the case among orna-
mental flowering plants, where each new variation in the
colour of the leaves or flowers is often sufficient to make the
plant attractive.
Careful investigation into the origin of the many varieties of
apples, pears, and other fruits leads to the conclusion that by far
the larger number of them are 'seminal sports' produced from
seeds casually sown in woods, hedgerows, and fields by birds or
'SEMINAL SPORTS' 307
self-sown in gardens : long ago they attracted the attention of
some one who considered the varieties worthy of cultivation.
Several of the more modern varieties of fruits have arisen as
'seminal sports' from pips or seeds selected in a haphazard
manner. Scarcely any of them l come true ' from seed ; the
peculiar characters which they exhibit are not hereditary; for
example, the seeds of a Cox's Orange pippin or a Worcester
Pearmain apple when sown do not produce trees bearing apples
of these kinds, neither do the seeds of the different varieties of
roses or carnations (except in rare instances) give rise to plants
bearing flowers similar to their parents. But in these cases, just
as in most perennial * bud-sports,' the fact that their characters are
not transmitted to seedling offspring is no drawback to their use-
fulness, for they can be and are readily propagated vegetatively.
'Seminal sports' are not unfrequent among annual plants;
in such instances, their peculiar character to be of use must
be hereditary, for there is no practical satisfactory method of
propagating these plants except by seeds. Numerous examples
of annuals are known in which the new characters presented
by them are transmitted, without material modification or altera-
tion, to all plants of succeeding generations derived from them.
Many of the best cereals are ' seminal sports ' of this class
vhich were originally discovered on some roadside or growing
imong the plants of an ordinary crop. The late Mr Patrick
>hirreff of Mungoswells, Haddington, Scotland, who introduced
everal new and excellent varieties of cereals into the market,
?as in the habit of systematically searching his fields of wheat
ind oats for plants presenting new and marked peculiarities of
;rain or straw, and although he attempted to raise new varieties
>y crossing and repeated selection as described below, his best
ntroductions appear to have been ' seminal sports ' discovered
n his fields with all their meritorious qualities ready-made and
ransmissible without change to their seedling offspring.
The sowing of large numbers of seeds, selected at random, of
he apple, pear, and other cultivated plants, in the hope that a
raluable variety may turn up suddenly, is a game of chance in
308 CULTIVATED PLANTS AND THEIR ORIGIN
which enormous odds are against the raiser; nevertheless, the
method has often led to successful results.
One of the best varieties of potato ever raised, namely, the
Magnum Bonum, was obtained by Mr James Clarke of Christ-
church, who found it among a batch of seedlings derived from a
promiscuously selected lot of potato * apples ' ; and many other
useful and ornamental varieties of cultivated plants have had a
similar haphazard origin.
In the case of a new form occurring among seedlings of
perennials, such as shrubs, fruit-trees, strawberries, potatoes,
roses and other plants which can be propagated vegetatively,
and also in the cases of those new forms of annual plants whose
peculiarities are completely and faithfully transmitted by seeds
to all their offspring, the work of the plant-breeder is reduced
to the mere propagation of the new variety.
Most frequently, however, it will be found that on sowing the
seeds of a new form or ' sport/ the majority of the seedlings do
not inherit the peculiar features of the parent but resemble the
original plants from which the parent * sported. 1 For example,
if in a batch of tomato plants bearing wrinkled inferior fruit, a
single individual were observed with superior smooth round fruit, it
would generally be found that a large number of the plants raised
from the seeds of such * seminal sport ' would have wrinkled fruit,
and none at all or only a few would bear smooth fruit. When a
new variety makes its appearance among crops propagated by
seeds, it is generally necessary not only to simply grow it, but to
take steps to ' fix ' the variety, so that all the seedlings raised from
it or from its descendants shall exhibit the peculiar characters
which make it worth the special attention of the grower. To
' fix ' and establish a new variety with constant characters from
such * seminal sports/ the following process of continued selection
is most frequently practised by seedsmen and other plant-breeders.
The seeds of the plant showing the new features are sown,
and those individuals of the offspring possessing the same
'SEMINAL SPORTS' 309
peculiar characters as the parent are allowed to produce
seed, all others being pulled out and discarded. The seeds of
this first selected generation are then sown, and a further
selection and sowing of those possessing the new attributes
is made. This process is repeated for several generations until
no weeding out is found necessary, that is until the new char-
acters become constant in all the offspring, after which the
variety is said to be 'fixed* and 'comes true' from seed. The
time taken to 'fix* a variety in this manner depends upon the
power which the plant possesses of transmitting its characters
to its offspring. This power is exceedingly variable and no
rules can be laid down in regard to it; in some instances 50
per cent, or more of the first generation may resemble the parent,
and, on sowing the seeds of these, 90 per cent, of the seedlings
may ' come true ' ; in such cases fixation of a new variety is
tolerably easy and may be effected in three or four generations.
In other cases the number of plants true to type in each succeed-
ing generation may be very small, and even after selection has
been carried on for many generations a large proportion of the
plants obtained at each sowing may possess none of the char-
acters of the variety which the plant-breeder wished to establish.
H. Vilmorin stated that some of his hybrid varieties of wheat
took six or seven years of cultivation and selection before they
were of sufficiently fixed character to be put on the market for trial.
The process applied to five or six generations of plants is
generally found to be sufficient to 'fix' many new varieties of
cereals, beans, peas, cabbages, turnips, tomatoes and other
annual and biennial plants; probably the raising and selection
of a similar number of succeeding generations of plants would
be needed to make a variety of a perennial plant c come true '
from seed. However, on account of the fact that several years
often elapse before seed is produced by many seedling perennials,
the process of fixing new varieties of such plants by selecting and
propagating in the above manner has rarely been carried out ;
22
310 CULTIVATED PLANTS AND THEIR ORIGIN
hence all our varieties of apples, pears, strawberries, tulips,
narcissus and many other cultivated plants do not ' come true '
from seed ; so far as their usefulness is concerned there is no
necessity for them to do so, for the single original sport, when
once obtained, may be propagated vegetatively by cuttings,
runners, grafts and bulbs. Of course, varieties whose peculiar
characters are not hereditary cannot be ' fixed ' at all. Varieties
which are the result of hybridisation often vary for many genera-
tions. On this account when fixation is being attempted , the
several generations raised for the selective process should be
protected or prevented as far as possible from crossing with other
varieties and with the untrue seedlings.
A knowledge of the Mendelian ' laws ' of inheritance is of great
assistance to the plant-breeder in his work of selection among the
offspring of hybrids.
Self-fertilisation or in-breeding, when not carried to an extreme,
tends to fix the characters of new varieties.
(b) Seminal or seedling varieties. As previously mentioned
no two seedling plants are exactly the same; even when they
are derived from seeds taken from the same pod they differ from
each other in one or more particulars. It may be that the
colour of the flowers is not exactly the same, or the form of the
leaf, the thickness of the root, or the size and habit of growth of
the stem may differ in different individuals. Where the variation
from the common type is obvious and distinct we have termed
the plant a c seminal sport ' ; seedlings showing lesser deviations
which are scarcely noticeable may be named ' seminal varieties!
Between a ' seminal sport ' and a ' seminal variety ' there is no
essential difference ; it is a matter of degree of variation only.
These very slight indefinable deviations from the common
type are of much importance, for experience teaches that many
of them may be vastly increased by selecting and cultivating the
plant in which the peculiarity is most marked in each successive
generation ; the development of the peculiarity and its fixation
go on simultaneously in such cases.
SEMINAL OR SEEDLING VARIETIES 311
For instance, if among a bed of plants whose flowers are
ordinarily purple a single individual is observed whose flowers
have a tinge of red, it is often possible to raise and fix a distinctly
red variety by selecting from each succeeding generation the plant
in which the redness of petals is most marked. Not only can
the tints of flowers be modified and increased, but almost all
other characters, however they may appear at first in the selected
plant, may be increased in a similar manner.
In, 1890 E. v. Proskowetz sowed in good garden soil seeds of
the wild sea-beet obtained from specimens growing on the south
coast of France. All the seedlings had much branched roots
like their wild parents, and sent up flowering shoots the same
year in which the seeds were sown : the average sugar-content
was low although it exhibited wide variation, namely, between
0*3 and 11*2 per cent.
The plants of this generation, with good sugar-content and
with thn least-branched and thickest roots were selected and
their seeds sown. The majority of the plants of this selected
second generation resembled their parents, but some of them
behaved as biennials and sent up no flowering stems in the first
year of their growth.
From these biennial forms a further choice was made and
their seed sown ; in consequence of the selection and good
culture, the roots in 1893 had an average sugar-content of 15*93
per cent, and each had an average weight of 426 grams. In
another series of selected plants the average sugar-content in
1894 was i6'99 P er cent, and the average weight of a root 368
grams. Although the seeds of these plants still gave rise to a
few annual plants resembling the original wild parents most of
the seedlings proved to be biennials, and in form of root and
amount of sugar greatly resembled some of the ordinary culti-
vated races of sugar-beet.
In order to determine to some extent how much of the
increased sugar-content and size of the root was due to the better
garden soil in which the plants were raised, and how much due
312 CULTIVATED PLANTS AND THEIR ORIGIN
to the selection of the best forms and the rejection of the worst,
another part of the garden was sown in 1890 with the wild seed
and the plants were allowed to remain and sow themselves down
year by year. The average sugar-content of the roots of the
latter rose year by year : in 1893 it was 4*5 per cent, in 1894
9-38, their average weight in 1893 was 147 grams and in 1894
232 grams. By a comparison with the previous figures it will be
seen that the process of selection had nearly doubled the sugar-
content and very considerably raised the average weight of each
root.
A. L. de Vilmorin by the selective process continued through
four generations, obtained from the slender-rooted annual wild
carrot (Daucus Carota L.) biennial plants having thick fleshy
roots resembling some of the ordinary types of cultivated carrots
in colour, form and size.
Professor J. Buckman is said to have raised the large hollow-
crowned * Student ' parsnip from the small-rooted wild parsnip*
by a similar process of selection.
These may be taken as instances of the rapid modification of
wild species by choosing and propagating by seed what are
considered the best specimens of several succeeding generations,
all other plants being rejected or destroyed.
Cultivated varieties now existing can be * improved 1 or
rendered more useful than they are at present in a similar
manner, and generally more easily than wild species.
4. Variations: how induced. From the foregoing account
it will be understood that the improvement of plants depends
primarily upon their variability ; for if plants were all alike, and
did not vary at all, there could be no selection. Moreover, in
plants raised from seeds, the variation must be hereditary, for
unless the peculiar quality or character possessed by a specially
selected individual plant is passed on to the next generation, the
selection becomes useless. For example, no progress can be
made in the development of a stiff-strawed race from a kind of
VARIATIONS: HOW INDUCED 313
barley or wheat with weak stems, by selecting and propagating
an individual plant with rigid straw, unless such stiffness is trans-
mitted to the descendants of the selected plant.
Which variations exhibited by plants are transmitted to their
seedling offspring, and which are not, can only be determined by
trial. The variations of plants and animals must arise from
specific changes in the constitution of their protoplasm, often
especially in the chromosomes of their nuclei, but in many in-
stances little certain knowledge is available regarding the nature
of these changes, and to cause a plant to vary with certainty in
some particular and desirable manner is at present impossible.
Even to make a plant vary at all appreciably is often a matter of
great difficulty, some species being very stable. However, when
variation once begins, the desired character very frequently
appears sooner or later among the plants, so that the first step in
plant improvement is to ' break the type,' or to make the type it
is intended to improve vary in any manner whatever.
Since the variations of plants are the starting points from which
improvement or modification begins, it becomes important to en-
quire if there are any^ methods by which variation can be induced.
Experience has taught that variation can be induced
(1) by varying the external conditions of life of the plant ;
(2) by crossing and hybridisation.
It is well known that an abundance of manurial constituents
leads to luxuriance of the various organs of a plant, while a re-
duction of these substances results in lowness of stature, and
general diminution of all parts ; poverty or richness of soil, there-
fore, leads to variation among plants. Similarly, the intensity of
the light, the warmth or coldness of the summer induces variations
in sweetness of almost all kinds of fruit. The size of the grains of
wheat, bar ley,, and other cereals, and that of many seeds and other
parts of plants, is also dependent on the cultivation of the ground
in which they are grown, and upon the season and the length of
time during which growth goes on: other external conditions
314 CULTIVATED PLANTS AND THEIR ORIGIN
bring about changes in the structure and function of various
organs of plants. Generally it may be said that variations of
this kind, induced by changes in the amount of food-constituents
in the soil, or by alterations of season and climate, are rarely, if
ever, hereditary ; they appear under certain conditions, but when
the conditions are altered the variations disappear.
For instance, by growing tall varieties of peas, beans, or any
other plants upon poor soil, successive generations of short
individuals may be obtained so long as the poverty of the soil
is maintained ; the seeds of such plants, however, when grown
upon good soil at once give rise to tall plants, showing that the
dwarfness of habit induced by such soil conditions is not a
permanent hereditary modification.
Wheat, oats, and other cereals, when grown upon good garden
soils, at wide intervals apart, as has been done by some propagators,
develop tall straw, long ears, and large grain, but no new permanent
variety can be produced in this manner.
By growing beets possessing ' fanged ' roots close together, they
have no room to develop their disfiguring branches, and may thus
be made to assume a good form ; nevertheless, seeds raised from
such plants, when grown under ordinary conditions of cultivation,
immediately give rise to plants with ' fanged ' roots like their
ancestors. When attempting to develop a new race of any kind
of plant, it is therefore important that the modification taken as
a basis upon which the selective process is carried out, should
not have arisen merely as the result of external conditions.
Where increased size of certain organs is the feature desired
in a new race, it is perhaps best to raise the successive genera-
tions of plants from which the selection is to be made upon a
moderately poor soil, rather than a specially rich one ; any in-
creased size of one plant over that of another under such circum-
stances would be less likely to be due to an accidental excess of
manure, and more likely to be due to an innate hereditary quality
of the plant.
VARIATIONS: HOW INDUCED 315
The most certain method of inducing variation in a plant is
to cross or hybridise it with another individual. In this process,
there is a mixing of the protoplasm of two distinct plants, and
the offspring therefore consists of living matter derived from two
distinct and unlike sources. Sometimes the plants of the first
and second generation obtained from such a cross all resemble
each other very closely. Succeeding generations, however, exhibit
very great variability, the plants showing the characters of the two
original parents blended in very variable degree, and peculiarities
not seen in the parents are very frequently observed among them.
The latter characters although apparently new are often those pos-
sessed by the grandparents or earlier ancestors of the plant which
have been transmitted in a latent state through several generations.
Variations which appear as the result of crossing are much more
frequently hereditary than characters produced by the action of
external conditions ; moreover, they can generally be increased
by selection. Not only is crossing of use for the purpose of in-
ducing variability among plants so that selection may be begun ;
it may be resorted to in order to combine in one variety of plant
characters previously possessed only by two different and separate
varieties. A tender variety which is of good quality in other
respects when crossed with a hardy kind of poorer quality, some-
times gives rise to one or more descendants, combining the good
quality of the former with the hardiness of the latter : similarly
other qualities of two distinct varieties may be blended, as in the
example of the crossing of pea plants with round green with
wrinkled yellow seeds, leading to the production of two new types,
namely, plants yielding round yellow and wrinkled green seeds
which breed true (see pp. 289-298). It must, however, be
observed that the combination of certain peculiarities in one and
the same plant cannot be attained by any means ; it is often
better to grow one variety for one purpose and another for another
purpose, rather than attempt the combination of antagonistic
features (see next paragraph).
316 CULTIVATED PLANTS AND THEIR ORIGIN
5. Correlated variability. The various parts of the body of
a plant or animal are so co-ordinated with each other that any
change in the structure or function of one organ very frequently
brings about some necessary change in another. The nature
of the connection between the correlated variations is in many
instances obscure ; nevertheless the existence of this kind of
variability must be always borne in mind by those who seek to
improve plants. Moreover, it is important that every endeavour
should be made to elucidate its nature, for a correct and
complete understanding of the structural and functional re-
lationships between the different parts of plants would enable
the plant-breeder to save much valuable time. There is little
doubt that through want of knowledge on such matters, plant-
breeders have not unfrequently attempted to do that which is
impossible.
In most cases quantity of produce and good quality are so
connected that beyond a certain point the increase of one brings
with it a decrease of the other, and to combine both characters
in maximum degree in one variety appears to be impossible.
For example, all attempts to obtain a race of sugar-beet with
the highest yield of roots per acre and highest known sugar-
content are found to fail when a certain percentage of sugar in
the root is reached \ with every increase of sugar-content beyond
this point there is invariably a decrease in size and weight of the
' root.'
It appears to be impossible to breed a wheat of richest
gluten-content, with as high a yielding power of grain per
acre as * rivet ' starchy wheat ; this difficulty is partially de-
pendent on the fact that the glutinous proteins are largely
stored in the outer layers of the endosperm which be-
come filled first, the central parts being filled up later
chiefly with starch ; the longer the assimilation goes on
the more starchy the grain becomes, and the larger the
crop*
DEGENERATION OF VARIETIES 317
Investigation has shown that thin-stemmed races of barley
always give the best quality of grain for malting purposes, and to
breed a variety combining the highest quality of grain with great
stiffness of straw is probably impossible.
It is generally known that seed-production and luxuriance of
vegetative organs are mutually antagonistic; for example, with
high yield of tubers of good quality, seed-production in the
potato has been vastly reduced, and in the case of oats and
wheat short-strawed varieties usually give a greater proportion of
grain than long-strawed kinds. A turnip of slow, long-continued
growth yields a greater dry weight per acre than a rapid-growing
variety, for there is a greater time for the manufacture, accumula-
tion and assimilation of food in the former than in the latter;
the attempt to produce a variety of turnip of rapid growth and
high feeding-value would fail after a certain point of excellence
was reached; fortunately in this case there appears plenty of
room for systematic work and improvement before the limit is
attained, and the same is probably true of practically all farm
plants.
6. Reversion, ' throwing-back,' atavism: degeneration of
varieties. A new variety of a plant becomes established
and ' fixed ' by destroying all those individuals of each
generation which do not resemble the general type. ' Fixation '
is, however, a relative term, for even in cultivated varieties in
which the process of destruction has been systematically carried
out and which have 'come true, 1 from seed during many
generations, t false plants' or Brogues' departing considerably
from the type appear among the offspring at irregular in-
tervals.
For example, individuals resembling the wild pansy ( Viola
tricolor L.) in form, colour and size of the flowers and leaves,
occasionally make their appearance among plants raised from
seeds of the best large-flowered cultivated types of pansy ; and
3l8 CULTIVATED PLANTS AND THEIR ORIGIN
among crops of green-topped turnips, purple-topped individuals
sometimes occur. * Rogues ' most frequently exhibit characters
possessed by the ancestors of the variety in which they are
found.
The tendency of plants to revert to long-lost characters is
termed atavism, ' thr owing-lack, or reversion. Some of the plants
which exhibit ( reversion ' to characters seen in remote ancestors
are doubtless Mendelian recessives, to which reference is made
previously (p. 299)*
Very few if any varieties of plants propagated by seeds remain
like the type first sent out by the raiser for more than a limited
number of years. In a great many instances where almost
everybody raises seed, destruction of * rogues' is not efficiently
or thoroughly carried out, and through the consequent mixing
with the progeny of the reverted plants, the type rapidly degener-
ates in purity.
Apart from the incompetence to distinguish slightly reverted
forms and laziness in carrying out their destruction, other changes
take place in the type through the different ideal which each
raiser of seed sets up before his mind when he selects the indi-
viduals to be employed as seed parents. For example, three
different raisers of seed of ' Gubbins' " Incomparable " pea ' are
almost certain to hold different views from Mr Gubbins and
from each other in regard to the relative importance of the
various characters of a good pea ; selection is therefore carried
out from three different standpoints, and in a few generations
the * Incomparable * variety no longer exists except in name,
unless Mr Gubbins himself also carries on the propagation : three
different types bearing the same name would arise. It is there-
fore very necessary for the farmer and gardener not to be led
away by the fascination of an old name, for it does not follow
that anything useful is obtained with it ; at the same time it must
be remarked that a new name does not necessarily represent
any new quality or character in the seeds to which it is applied ;
DEGENERATION OF VARIETIES 3*9
new names may easily be applied to old articles when the latter
cannot be sold by their original names.
Much valuable experience can be gained by growing small
trial plots of several differently named varieties of farm and
garden plants of the same species.
Moreover, a useful lesson can be learnt by sowing small plots
of seeds of a variety of turnip, pea or other plant bearing the
same name and obtained from half a dozen different firms
of seedsmen. Farmers rarely do enough testing of this
kind,
PART IV.
CLASSIFICATION AND SPECIAL BOTANY
OF FARM CROPS.
CHAPTER XXIV.
THE CLASSIFICATION OF PLANTS.
i. SYSTEMATIC or Classificatory Botany is concerned with the
naming, describing and arranging of plants into groups.
Various systems of classification have been proposed from
time to time, the one which has superseded all others being the
so-called Natural System. Underlying it is the assumption that
all the different kinds of plants on the face of the earth have
been derived by natural descent from a few ancient ancestors,
and the object of this system is the arrangement of plants into
groups according to their affinity or blood-relationship.
The evolutionary history and genetic affinity of plants can
never be known accurately, and there are no universal rules by
means of which the relationship of organisms can be determined
with certainty. However, in forming the groups into which the
Vegetable Kingdom is divided, botanists endeavour to take into
consideration as many peculiarities or characters of the plants as
possible, and place together only those which agree in a number
of characters^ it is reasonably contended that by this method
plants which are related to each other by descent are likely to be
brought together.
a. The terms employed to denote the different groups are
indicated below.
GENUS: PLANT-NAMES 321
Individual and species: variety and race. When a red
clover seed is sown and allowed to grow it produces a single
plant, which after a time gives rise to a number of seeds, each ot
which can grow and produce ofTspring similarly, so that in a
few years a very large number of individual red clover plants
may be obtained. It will be found that these individuals,
although not exactly like each other, are nevertheless very
similar in the form, colour, size and other features of their roots,
stems, leaves and flowers. Such plants, and all those upon the
face of the earth which resemble them to such an extent that
they may be considered to have descended from a common
ancestor, are grouped together by botanists, the whole group
being termed a species.
While the majority of the characters possessed by the various
organs of a species are constant, certain features, such as the
hairiness of the leaves and stems, or the colour of their flowers,
may vary: thus we may find in a field of red clover, plants
bearing white flowers instead of purple ones : such are described
as varieties of the red clover species. The peculiar characters
of a variety are usually transmitted to few or none of its
descendants.
Varieties presenting some considerable variation from the
most prevalent characters of the species are termed sub-species or
races when the variation is known to be hereditary for many
generations.
Many of our cultivated crops are permanent varieties, or races
developed by the process of selection (see chap, xxiii.) from wild
species.
Genus: plant - names. Even cursory examination of the
various species of plants commonly met with, reveals the fact
that a certain number of them resemble each other, especially
in the form, arrangement and number of the parts of the flower.
Thus, red clover, Alsike clover and white clover, although differ-
ing from each other in the colour of their flowers and in the
322 THE CLASSIFICATION OF PLANTS
shape, size and habit of their vegetative organs, are nevertheless
very similar in the construction and form of their flowers.
Species possessing such close resemblances in the structure
and arrangement of their reproductive organs are grouped to-
gether and are spoken of as a genus.
The scientific or botanical name of a plant consists of two
Latin words, the first of which indicates the genus and the second
the species to which the plant belongs. For example, the true
clovers constitute the genus Trifolium, the species red clover
being named Trifolium pratense, while Alsike clover is known
as Trifolium hybridum. Similarly the various species of butter-
cups collectively form the genus Ranunculus, two common species
of the genus being Ranunculus repens (creeping crowfoot) and
Ranunculus bulbosus (bulbous buttercup).
As the same species has sometimes been named differently by
different botanists and the same name has not uncommonly
been used for two or more distinct species, to prevent confusion
it is customary in systematic works to add to the name of the
plant the full or abbreviated name of the botanist who gave the
plant its name and described it.
For example, the name Bellis pertnnis Linn, or Bellis pertnnis
L., indicates that Linnaeus gave the name and it also implies
that the plant denoted is the particular species which Linnaeus
described under this name.
Just as species are grouped into genera, so are genera re-
sembling each other grouped into Orders or Families.
Orders possessing similar characters form Classes, and classes
having common distinctive characters are finally grouped together
into Divisions.
Where some of the representatives of a Genus, Order, Class*
or Division possess characters which mark them off more or
less distinctly from the rest of the group to which they belong,
it is sometimes useful to subdivide these groups into Sub-genera,
Sub-orders, Sub-classes and Sub-divisions.
THALLOPHYTES 323
3, The following are the chief Divisions of the Vegetable
Kingdom :
Division I. Myxomycetes,
II. Thallophyta.
III. Bryophyta.
IV. Pteridophyta.
V, Spennatophyta.
The plants included in the first four divisions are often spoken
of as Flowerless plants or Cryptogams. Among them repro-
duction is carried on chiefly by means of minute one-celled
bodies termed spores > which are set free from the parent plant
and afterwards germinate and give rise to new plants.
The Spermatophytes (Division V.) were formerly designated
Flowering plants or Phanerogams. In these, reproduction is
carried on chiefly by means of seeds, each of which contains an
embryo-plant.
Division I. The Myxomycetes are commonly known as
slime-fungi. In a vegetative state the bodies of these organisms
consist of naked masses of protoplasm termed plasmodia^ and
are capable of creeping about in a manner similar to the
movement of an ordinary amoeba. The Myxomycetes are devoid
of chlorophyll, and almost entirely saprophytic, that is, they
feed mainly upon decaying organic remains, many species being
common upon rotten wood and dead leaves. In several respects
they greatly resemble the lowest forms of the animal kingdom,
and are by some authorities included in the latter and spoken
of as Mycetozoa, or fungus-animals : their method of reproduc-
tion by means of spores is, however, similar to that prevalent
among certain Fungi.
One organism generally included in this division and described
in chapter Hi., is parasitic, and the cause of the disease known
as ' Finger-and-toe ' or * club-root ' among turnips and cabbages,
Division II. The Thallophytes are plants, such as sea-weeds,
324 THE CLASSIFICATION OF PLANTS
lichens and toad-stools, the bodies of which are of simple
construction and exhibit no differentiation into stem, root and
leaf. When branching does take place, the members produced
are usually all essentially alike, and resemble the previously
existing parts from which they arise : the body of a plant of
such simple structure is termed a thallus. In some instances
each plant is very minute, being merely a single cell, while in
others, the thallus consists of thousands of cells : in all cases,
however, the cells possess a distinct cell-wall.
The Thallophytes are divided into several sub-divisions of
which two, namely, the Sehizophyta and the Fungi are of
great practical importance : the former includes the Bacteria
or Schizomycetes.
Division III. The Bryophytes comprise two classes of plants,
namely, liverworts and mosses.
Division IV. The Pteridophytes include ferns, horsetails
and club-mosses.
Some of the above divisions of the Vegetable Kingdom, such
as those including the sea-weeds, mosses and ferns, are without
practical interest or importance for the farmer, and want of
space prohibits more than a mere mention of their existence.
Students wishing for information in regard to those divisions are
referred to the ordinary text-books of systematic botany.
The Bacteria and Fungi, however, which are included in the
Thallophyta, need special attention on account of their practical
bearing, and are dealt with in subsequent chapters.
Division V. The Spennatophytes or Phanerogams include
all those plants which produce seeds. This division is split up
into two sub-divisions namely :
Sub-division i. Gymnosperms.
and Sub-division 2. Angiosperms.
In the Gymnosperms, of which the cone-bearing firs and pines
are examples, the carpels are flattened structures and the ovules
CHORIPETALJE 325
and seeds lie naked or exposed on the surface of the latter:
fertilisation is effected by pollen-grains which come into direct
contact with the micropyle of the ovule.
The Angiosperms possess carpels which are hollow closed
structures, the ovules and seeds being developed within the
completely closed cavity or ovary of the carpels. In these plants
the pollen-tube must first pass through the tissues of the carpels
before reaching the ovule.
4. As practically all farm plants belong to the Angiosperms it is
important to enter into greater detail in regard to the classification
of this sub-division of the Vegetable Kingdom. The following is
an outline of the arrangement and chief features of the Classes,
Sub-classes, and a few common Orders included in it.
Sub-division 2. ANGIOSPERMS.
Glass I. Dicotyledons. In these plants the embryo has two
cotyledons and the floral-leaves are usually in fours or fives. In
a cross-section of the stem the vascular bundles appear arranged
in a single ring round a central pith and in perennial species
concentric zones or * annual rings ' of wood are present, the
* annual rings ' being formed by a cambium-tissue. The leaves
are generally net-veined.
Sub-class I. Choripetal. The corolla when present is poly-
petalous.
In some plants of this sub-class the flowers are imperfect;
either the corolla or calyx is absent or both parts of the
perianth are missing.
(i) Flowers regular, hypogynous y usually with a single green or
white perianth : fruit one-seeded.
Order. Cannabacca (see p. 332).
Order. Polygonacea (see p. 350). Flowers small with a perianth
of three to six tree segments : stamens five to eight opposite the
perianth segments ; gynsecium of two or three united carpels, the
ovary generally triangular or oval in section, and containing a single
23
326 THE CLASSIFICATION OF PLANTS
erect ovule ; fruit an angular nut ; seed endospermous. The
stems are mostly herbaceous and bear alternate leaves, which
possess membranous tube-like stipules (the ochrece) clasping the
stem. Common plants of this Order are Dock and Sorrel
(Rumex), Knot-grass (Polygonum aviculare L.), Black Bindweed
(Polygonum Convolvulus L.), and Buckwheat (Fagopyrum Sagit-
tatum Gilib.).
Order. Chenopodiacea. This Order which is described in
chapter xxvii., possesses close affinities with the CaryophyllacecB
mentioned below.
(2) Flowers, usually with both calyx and corolla present.
(a) Flowers hypogynous : gynascium apocarpous.
Order. Ranunculacece. Flowers mostly regular, with free
sepals, numerous stamens and one or many free carpels. The
fruit is an achene or a follicle. Most plants of the Order are
herbaceous and contain acrid poisonous j uices. Common examples
are Buttercups (Ranunculus), Columbine (Aquilegia), Monkshood
(Aconitum), and Anemone.
(b) Flowers hypogynous : gynaecium syncarpous.
(i) Ovules on a free-central placenta.
Order. CaryophyllacecB, Flowers regular with four or five
persistent sepals and the same number of petals : stamens usually
eight or ten ; fruit a capsule with few or many endospermous
seeds. The stems have opposite leaves and thickened nodes
and the flowers are generally pink or white. Common examples
are Pinks and Carnations (Dianthus), Campions (Lychnis), Chick-
weed (Stellaria), and Spurrey (Spergula).
(ii) Ovules on parietal placentas.
Order. Papaveracecs. Flowers regular with two sepals, four
petals and many stamens. Fruit a capsule dehiscing by pores
and containing many small endospermous seeds. Plants belong-
ing to this Order contain milky or coloured latex and are often
poisonous : poppies are common examples.
Order. Cruci feres (see p. 371).
(iii) Ovules on axile placentas.
Order. Linacea (see p. 395).
SYMPETAL^: 327
(f) Flowers perigynous : gynaecium superior and apocarpous.
Order. Rosacece (see p. 403).
Order. Leguminosa (see p. 416).
(d) Flowers epigynous : gynaecium inferior and syncarpous.
Order. Umbellifera (see p. 447).
Sttb-Class II. Sympetalse. Corolla gamopetalous.
(1) Flowers hypogynous.
(a) Corolla regular.
Order. Boraginacea. Flowers with a five-lobed calyx and a
five-lobed corolla; stamens five; gynsecium of two united carpels ;
the ovary is four-lobed and four-chambered with a single ovule
in each chamber ; fruit a schizocafj) which splits into four
nut-like mericarps. Examples of plants belonging to this order
are Comfrey (Symphytum\ Borage (Borago\ and Forget-me-not
(Myosotis).
Order. Solanacea (see p. 462).
(b) Corolla irregular zygomorphic.
Order. Scrophulariacea. Flowers with a five-lobed calyx and
a four- or five-lobed corolla ; stamens epipetalotrs, generally four,
with a rudimentary fifth ; gynaecium of two united carpels ; ovary
two-celled ; fruit a capsule, containing many endospermous seeds.
Common representatives of the order are : Snapdragon (Antir-
rhinum)^ Foxglove (Digitalis)^ Speedwell (Veronica), Yellow-
Rattle (Rhinanthus\ and Eyebright (Euphrasid).
Order. Labiate. Flowers with a five-partite ribbed calyx,
and a two-lipped zygomorphic corolla; stamens two or four,
didynamous, epipetalous ; gynaecium of two united carpels ; ovary
four-celled, with one ovule in each cell ; fruit a schizocarp
splitting into four nut-like mericarps. The stems of the plants
are four-angled, and bear opposite or whotled leaves. Common
examples are Mints (Mentha\ Self-heal (Brunclla or Prunella),
Dead-nettle (Lamium).
(2) Flowers epigynous.
Order. Composite (see p. 476).
328 THE CLASSIFICATION OF PLANTS
Glass II Monocotyledons.-^-The embryo of these plants has
only a single cotyledon, and the floral-leaves are in threes or
fours, never in fives. A cross-section of the stem shows a
number of isolated vascular bundles, not in a single ring but
usually scattered and without any distinct central pith: no
cambium is present in the stems. The leaves are usually
parallel-veined.
(1) Perianth absent or represented by small scales or bristles.
Order. Graminea (see p. 481).
Order. Cyperacea. Flowers unisexual or bisexual, arranged
in spikelets, eath flower in the axil of a small bract (glume).
Perianth none or consisting of three to six bristles; stamens
generally three ; gynaecium syncarpous, with a one-celled ovary
and a single style, with two or three simple filamentous stigmas ;
ovule one, erect The fruit is a three-sided or flattened nut
containing a single endospermous seed which is generally free
from the pericarp. The plants of this Order are often confused
with grasses, but have mostly solid triangular stems and entire
leaf-sheaths.
Common examples are the Bulrush (Sdrpus\ Cotton-grass
(Eriophorum), and Sedge (Carex).
(2) Perianth present and regular,
(a) Gynaecium superior.
Order. Liliacece. Flowers with a six-partite coloured perianth :
androecium of six stamens.
Common plants belonging to the Order are Lily-of-the-valley
(Convallaria majalis L.), Ramsons (Allium ursinum L.), and
other species of 'Garlic* (Allium\ Hyacinth, Tulip and Meadow
Saffron (Colchicum autumnale L.).
Order. Juncacea. flowers small with a six-partite green or
brown perianth, andrcecium usually of six stamens. Fruit, a one-
or three-celled capsule.
Common examples of the Order are various species of Rush
(Juncus) and Wood-rush (Luzula) (see p. 620).
MONOCOTYLEDONS 329
(b) Gynaecium inferior.
Order. Iridca. Flowers with a six-partite brightly coloured
perianth: androecium of three stamens, the anthers of which
open outwards ; gynaecium syncarpous, three-celled, the simple
style often surmounted by three leaf-like coloured branches on
which are the stigmas. Fruit a capsule containing endospermous
seeds. Common plants of the Order are Yellow flag (Iris
Pseud-acorus L.), Crocus and Gladiolus.
Order. Amaryllidea. Flowers with a six-partite coloured
perianth : androecium of six stamens, the anthers of which open
inwards. The gynaecium and fruit resemble those of the Iridea.
Common examples are Daffodil (Narcissus) and Snowdrop
(Galanthus\
(3) Perianth present ) cpigynous, and zygomorphic.
Order. Orchidca. Flowers irregular, generally with one stamen,
which is united to the style. Gynaecium inferior, ovary mostly
one-celled with parietal placentas. The fruit is a capsule con-
taining a large number of very minute seeds. Common ex-
amples are Purple Orchis (Orchis mascula L.), Spotted Orchis
(Orchis maculata L.) and Tway-blade (Listera ovata Br.).
Ex. 172. Students should describe as many common plants as possible,
taking their parts in the order indicated below.
(i) Habit and general appearance. Whether annual, biennial or perennial ;
herbaceous or woody.
(ii) Root. Fibrous or with a distinct tap-root ; presence or absence of
adventitious roots.
(iii) Stem. Herbaceous or woody ; erect, decumbent, prostrate, or wind-
ing, &c. ; shape in transverse section, square, round, ribbed, &c. ; hairy,
spiny, with harsh or hispid hairs, or glabrous : colour.
(iv) Leaf. Radical or cauline ; opposite, whorled or alternate; simple or
compound ; if compound, pinnate or palmate ; stipulate or exstipulate ; sessile
or petiolate ; shape of blade or leaflets ; character of the margins and tips ;
smooth or hairy surfaces.
(v) Inflorescence. Definite or indefinite; kind; presence or absence of
bracts and bracteoles.
(vi) Flower. Complete or incomplete ; regular or irregular ; tygomorphic
or actinomorphic.
330 THE CLASSIFICATION OF PLANTS
(vii) Calyx. Inferior or superior ; polysepalous or gamosepalous ; number
and form of the sepals or lobes of the calyx.
(viii) Corolla. Hypogynous, perigynous or epigynous ; polypetalous or
gamopetalous ; number, form and colour of petals or lobes of corolla.
(ITU) Andraecium.'^ Hypogynous, perigyuous, epigynous or epipetalous ; free,
monadelphous, diadelphous, polyadelphous or syngenesious ; di- or tetra-
dynamous.
(x) Gynacium. Superior or inferior ; apocarpous or syncarpous ; number
of carpels, styles and stigmas ; if syncarpous, whether ovary is one, two or
more celled ; ovules on axile, parietal or free central placentas.
(xi) Fruit. Dry or succulent ; indehiscent, splitting or dehiscent ;
kind.
The following may be taken as an example of plant description :
Bulbous buttercup (Ranunculus bulbosus L.).
Habit. A hairy perennial with bulbous rootstocks, erect stems about a
foot high, divided leaves and yellow flowers ; common in meadows and
pastures.
Root* Fibrous.
Stem. Herbaceous, lower part bulb-like, branches erect ; peduncles
furrowed.
Leaves. Radicle and cauline; cauline leaves alternate; simple, exstipulate ;
lower leaves with long petioles ; upper leaves cut into narrow segments ; the
blade cut irregularly into three lobes which are tri-partite.
Inflorescence. Definite ; the main axis and its branches, each end in a single
flower.
Flower. Complete, actinomorphic.
Calyx. Inferior, polysepalous, five sepals, reflexed.
Corolla. Hypogynous, polypetalous, five petals, yellow, each petal with a
nectary at its base.
Andrcecium. Hypogynous j stamens free and indefinite.
Gynacium. Superior, apocarpous, carpels many spirally arranged on a
conical receptacle.
Fruit. Many tree achenes.
Ex. 173. After describing the plants as in previous Ex., their position in
the Vegetable Kingdom should be assigned in accordance with the following
scheme :
(i) Division.
(ii) Sub-division.
(iii) Class.
(iv) Sub-class*
(v) Order.
(ri) Genus.
(vii) Sptcitt.
MONOCOTYLEDONS 33 1
The position of the bulbous buttercup is represented thus*
Division : Spermaphyte.
Sub-division : Angiosperm.
Class: Dicotyledon.
Sub-class: Choripetalac.
Order: Ranunculacex.
Genus: Ranunculus.
Species : bulbosus.
CHAPTER XXV.
OANNABACEJE.
i. General characters of the Order. Flowers unisexual ; dioe-
cious. '
Male flowers with a five-leaved perianth and andrcecium of
five stamens, the filaments of which are erect in the flower-bud.
Female flowers hypogynous, with a small entire cup-shaped
perianth surrounding the ovary. The gynaecium possesses a
one-celled ovary with a single ovule within; styles two, decidu-
ous, long and papillose. Fruit, a form of nut, dry, indehiscent,
containing a single, pendulous seed. Seed with a curved or
spirally-rolled embryo and very small reserve of endosperm.
This is a very small Order containing but two genera and
three species. It is often treated as a sub-order of the Urticaceae
or nettle family. The flowers are wind fertilised.
The plants representing the whole Order are The Common
Hop (Humulus Lupulus L.) ; Japanese Hop (Humulus japonicus
Sieb. et Zucc.) ; and Hemp (Cannabis sativa L.).
2. The Japanese Hop (Humulus japonicus Sieb. et Zucc.) is an
annual sometimes grown in gardens as an ornamental climbing
plant on account of its rapid growth. It resembles the Common
Hop in its stems and leaves, but the female inflorescences or
strobiles contain no ' lupulin ' and are consequently useless for
brewing purposes.
3. The Common Hop (Humulus Lupulus L.) is a perennial
herbaceous plant, cultivated almost entirely for the female in-
florescences, which are employed in the manufacture of beer.
It is probably indigenous in the British Isles, but most of the
882
THE COMMON HOP
333
so-called wild hops so frequent in the hedges in the south of
England, are no doubt generally escapes from cultivation or
seedlings from cultivated plants in the neighbourhood.
The short young shoots are occasionally utilised as a substitute
for asparagus, and from the ' fibre ' of the stem a coarse kind of
cloth can be made, but these uses of the plant are of no practical
importance.
SEED AND GERMINATION. In autumn the female inflor-
escences or 'hops,' if left on the
plants, readily break up, and the
bracts (mentioned below) to which
the fruits are attached are carried
some distance by the wind. The
single seed within each fruit con-
tains a spirally curved embryo,
which germinates only after a rest
during the winter. In spring the
young plants appear above ground,
and possess two narrow strap-
shaped cotyledons (Fig. 103).
ROOT. The primary root of a
seedling hop produces several
r Root; Ahypocotyi;, cotyledon. branches which goon equal ft fc
thickness. From all the thicker roots a great abundance of
hair-like fibrils are given off.
A striking feature in both old and young plants is the exceed-
ingly large root-system which they possess in comparison with the
parts which come above ground. The thicker roots are covered
with a mass of loose reddish-brown bark. Some of them penetrate
to very great depths in the ground, entering cracks and openings
wherever the subsoil is rocky ; others remain nearer the surface,
and spread horizontally in the upper layers of the soil, giving
rise at the same time to an enormous number of fine fibrils.
Adventitious roots are abundant on the underground stems.
FIG. 103. i. Seedling hop, one week
old. 2. The same, two weeks old.
334 CANNABACE^
THE STEM. The stems, which are generally termed 'bines, 1 are
herbaceous, angular and hollow, and of variable colour, being, in
some varieties, purplish-red, in others pale green, or green streaked
with red. They make their appearance in spring from buds of
the underground perennial * rootstock ' or rhizome, and die
down in autumn. The lower part, however, of each ' bine '
below ground does not die, but thickens and forms a further ex-
tension of the * rootstock/ The * sets ' used in propagating the
plant are these thickened underground parts of the stems ; they
are cut off the parent plant in spring, and readily form adventi-
tious roots when planted. The herbaceous stems above ground
bear thin opposite lateral branches, which are of considerable
length about the middle of the main stem. It is upon the
lateral branches that the female inflorescences are produced,
hence their formation and preservation is of the utmost import-
ance to the hop grower.
The stems, although too weak to stand erect by themselves,
are able to wind round any support such as a pole, a piece
of stretched string or wire, or another plant placed near them,
and frequently reach in this manner a height of 25 or 30
feet. In ascending a support the free tip of the stem slowly
moves round in a circle, from left to right, in the same direction
as the hands of a watch. The most rapid growth in length takes
place when the support is upright, and in stems growing erect
the internodes are longer than upon stems which are allowed to
grow along a string inclined away from the vertical. The
growth continues for a longer period, and is more even in its
rate on sloped supports than on erect ones. When the support
is inclined at an angle of between 45 and 60 degrees away from
the vertical, the stems are unable to climb satisfactorily without
external aid, their tips needing to be trained or assisted to
wind, otherwise they hang away from the support. In all kinds
of hop, but especially in the wild and coarse cultivated varieties,
the "stems and also the leaf petioles and main 'veins' have
THE COMMON HOP 335
several lines of strong hooked hairs which make the plant rough
to the touch, and help it to cling to its support
THE LEAF. The hop has opposite leaves which vary con-
siderably in shape even on the same stem. To some extent the
variation depends upon the position on the stem and the age
and variety of the plant. Upon young seedlings and on the
youngest upper branches of older hops they are mostly cordate,
with a deeply serrated margin. On older parts the leaves are
large and broad, generally palmately three or five lobed, with
deep acute serrations. Each possesses a petiole about half as
long as the blade, and is stipulate ; the stipules of opposite
leaves are united and broadly triangular.
THE INFLORESCENCE AND FLOWERS. The hop plant is
dioecious, the male flowers, growing upon one individual plant,
while the female ones occur upon another. Occasionally ex-
amples are found which are monoecious, that is, both kinds of
flowers are present upon the same plant.
a. The inflorescences bearing the male flowers are much
branched cymose panicles, which grow either from the axils of
the main stem or from the axils of the lateral shoots.
Each MALE FLOWER is about a quarter of an inch in diameter,
and possesses a five-leaved sepaloid perianth, opposite which are
five stamens. The latter have very fine short filaments and long
anthers, which dehisce by slits opening most widely at the apex
(*/, Fig. 105).
b. The inflorescences of female flowers somewhat resemble
fir cones in external appearance, and are borne on branches which
arise either directly from the leaf axils of the main stem itself
or from the axils of the leaves upon lateral shoots produced by
the main stem, They are spoken of as strobiles (A, Fig. 104),
and are the * hops ' of commerce.
A fully developed strobile when ripe possesses a long central
axis covered with fine downy hairs, and is popularly termed the
' strig ' of the ' hop ' in Kent (B, Fig. 104).
336
CANNABACE^B
Upon opposite sides of the latter are alternate pairs of 'stipular
bracts' (sl>) which appear to form four rows along its entire
length. Each pair of these ' stipular bracts ' is in reality a pair
of stipules belonging to a leaf which has not developed a blade.
In some hops, however, notably the coarser varieties, an excess of
nitrogenous manure leads to the monstrous development of the
missing leaf-blades and the scaly bracts of the hop strobile appear
interspersed with small green leaves, a pathological condition
which is to be avoided.
D
FIG. 104. A, Hop strobile or female inflorescence. s& ' Stipular bract ' ; b bracteole.
5, Axis of the strobile (the ' strig '). a The main axis j d the cymose branches of
! axis on which the female flowers are borne ; sb point of insertion of * stipular bract ' ;
FIG. 104.-
, A *
the axh
b point where bracteoles are attached (see D).
C, Piece of axis of the strobile showing the disposition of the ' stipular bracts ' s&, and
the bracteoles b.
DI Same as C, with the stipular bracts and one bracteole removed.
In the axil of the true bract, and therefore appearing to arise
at a point on the main axis opposite the gap between a pair of
its stipules, is a very short cymose axis (d) upon which four
female flowers arise. Each flower is subtended by a bracteole (b)
whose base partially envelops the former.
The bract-like stipules and bracteoles are popularly termed
' petals ' by hop growers.
THE COMMON HOP
337
The FEMALE FLOWER is very minute (4, Fig. 105), and pos-
sesses a cup-shaped perianth (c) with an entire edge. The ovary
is superior, and contains a single pen-
dulous seed. Two long styles (s)
are present, each covered from end
to end with small elongated papillae.
The FRUIT (6, Fig. 105) is oval,
about the size of a white mustard seed,
indehiscent, and generally described
as a nut, although it is superior.
The SEED possesses a curved em-
bryo and a very small amount of
endosperm. When the strobile or
female inflorescence is very young
the * bracts ' are small and scarcely
visible except those near its base.
The stigmas of the flowers, however,
the hop. 's Perianth (sepal) ; st sta- are very conspicuous, and form the
T'perianth of male flower with SO-Called ' brush ' of the hop.
anthers of the stamens removed; the rrii i , j , i , i >
short filaments are visible. The plants are said to be * in burr
^^^r^^^ when the strobiles have reached this
jMjyta., the brush ' of the flowers stage O f development.
entire"cup?!?ke peT^ Soon afterwards the stigmas con-
sty 5 ! e Abra C teoi e w surrounding the stituting the ' brush ' drop off, and
ripe fruit. /The corolla ; o apex of about the same time a rap j d growth Q f
6. The ripe fruit (a nut). the bracts takes place The stro bil e
then begins to assume its characteristic shape of a fir-cone, and
at this period the plant is said to be ' in hop/
Although the bracteoles develop to a considerable extent and
the hop * grows out/ even when the flowers in their axils are
unfertilised and abortive, nevertheless the largest bracteoles in
a ' hop ' are those in whose axils fertile fruits are present : the
fertilisation of the ovule, to a certain extent, stimulates the growth
of the bracteole subtending the flower.
5 6
FIG. 105. T. Single male flower of
338 CANNABACE^E
The ' Lupulin '-Glands of the Hop. In the interior of a
full-grown hop strobile are seen a large number of golden-yellow
pollen-like grains attached to the outer surface of the bracteoles,
especially near their bases. The perianth surrounding the fruit
is also studded with them, and a smaller number are present
upon the bases of the bract-like stipules. They are not met
with upon the ordinary leaves or stems of the plant. When
hops are shaken or knocked about these small grains are easily
detached, and may be obtained in the form of a bright yellow
powder sometimes spoken of as * hop-meal 7 or * lupulin'
Among hop-growers this powder is often designated the c con-
dition ' of the hop, and so far as a brewer is concerned the chief
value of a sample depends upon the amount and nature of the
' hop-meal ' present in it, all the rest of the hop, such as its
axis, bracts, and fruits, having little more than an indirect and
comparatively small value in the production of beer.
In an unripe ' hop ' the ' lupulin ' particles are brilliant and
transparent, of a golden yellow hue. As the ' hop ' ripens they
lose their transparency, becoming opaque, and assume a pale
sulphur or citron yellow colour. This change in transparency
of the 'lupulin,' which is easily observed with a pocket lens, is
the best criterion of the ripeness of a hop. In practice hops are
generally picked unripe ; they should, however, be left until a
Few opaque citron yellow particles are seen interspersed among
the transparent ones on the lower bracteoles.
When rubbed between the finger and thumb, the ' lupulin'
feels oily, and emits a characteristic odour which, in the best
varieties, is somewhat pleasant, while in the less valuable coarser
kinds the odour resembles that of garlic.
Each particle of * hop-meal ' or ' lupulin ' has the form and
structure given in Fig. 106. It originates from a single epidermal
cell, and at the time the 'hop* is just showing the * brush,
appears in the form of a hollow cup supported on a very short
stalk, consisting of two or three cells (2, Fig. 106). The cup is
THE ' LUPULIN '-GLANDS OF THE HOP
339
one cell thick, and each cell possesses a thick cuticle, dense
protoplasmic contents, and a well marked nucleus. Before the
hop has quite assumed its cone-like shape, the cells of the cup
begin to produce a secretion which collects within the substance
of the upper cell-wall of each
cell, and gradually lifts up the
cuticle much as the skin is lifted
up by matter in a blister.
As more and more of the
secretion is poured out by the
secretory cells the hollow space
of the cup becomes filled up with
it, and the cuticle which covers
the secretion as a fine thin skin
is bulged out above the margin
of the cup, as at Fig. c, 106. The
outline of the cells is seen upon
the cuticle.
3. Fully developed gland, s Secretory .
cells; c cuticle. The whole structure arises from
4. Vertical section of 3. s Secretory . , . ,
cells; c cuticle; o cavity filled with resin the epidermis of the bracts, and
and oily contents. . - P . . .. t . .
is a form of multicellular hair.
On account of its power to secrete it is termed a gland or
glandular hair. The connection of each gland with the surface
of the bract is very small and delicate only the width of one
or two cells consequently they are readily broken off when
touched.
By rough treatment on the hair-floor where the hops are dried,
and also by careless shovelling when on the ' cooling ' floor, the
hops often become broken, and a considerable loss of these
valuable glands takes place. For the nature of the secretion
contained in the glands, see p. 346.
VARIETIES. So far as names are concerned a very large number
of varieties of hops are grown in England. Many of them, how-
ever, exist only in name, the same variety passing under dif-
3 4-.
FIG. 106. Lupulin-gland of the hop
(magnified).
1. On very young hops in 'burr ' stage.
2. Vertical section of i.
340 CANNABACE^E
ferent names in different localities or on distinct farms. Only
a small number of distinct kinds are in existence ; they vary
in length and colour of 'bine/ hardiness, period of ripening,
and quality of the 'hop/
A Good Hop. The undermentioned points are of import-
ance in estimating the quality of any variety of hop in a natural
fresh state :
(1) The yield should be good, and the plant should be
hardy and capable of resisting the attacks of mould and aphis.
(2) The ' lupulin '-content of the strobiles should be high ;
the ratio of the weight of the ' lupulin ' to the weight of the rest
of the strobile (its ' petals/ axis and fruits) should be as great as
possible.
(3) The aroma should be fine. It is not possible to define
this point, but it must be observed that the best prices are only
paid for those hops whose odour is agreeable and free from any
smell resembling that of onions or black currant shoots.
(4) In the best varieties the stipular bracts of the strobile
are generally smooth and broad, while those of the. coarser
less valuable kinds, with poor aroma, are narrow and almost
always ribbed, appearing as if puckered or crumpled.
(5) The stipular bracts and bracteoles in the fine varieties
are thin and firm, and packed closely upon the axis of the
strobile. The more ' petals ' per inch of ' strig ' or axis the
better the 'hop/ The axis should be thin, and the fewer the
matured fruits with seeds within them the better, as the seeds
are said to impart an unpleasant flavour to beer.
(6) When quite ripe the natural colour of those varieties
which sell for the highest prices is a pale golden yellow with
a faint tinge of orange : the less valuable early sorts are deeper
yellow with darker greenish stipular bracts.
In order to preserve the ' hops ' after picking they are dried
in specially-constructed kilns, and during the drying process are
subjected to the action of the fumes of burning sulphur (sulphur
MID-SEASON OR MAIN CROP VARIETIES 341
dioxide gas), which bleaches and very considerably modifies their
natural tint : the greatest alteration, due to this treatment, takes
place in unripe hops. The colour of English commercial
samples is therefore unlike that of the natural hop.
The following are the chief kinds of hops grown in this
country :
A. Early Varieties
Prolific and Mtopham.
These hops have red bines, and long coarse strobiles of poor
quality which, when ripe, have a somewhat orange or brownish
tinge. They yield good crops, and usually ripen in the order given.
Early Hobbs\ An early hop resembling the Prolific, but
smaller with a green bine.
Henhanfs Jones. An oval medium-sized hop, thin in * petal*
and poor in lupulin, but of good colour and aroma. This name
is often applied incorrectly to the Meopham and
similar coarse hops.
Bramling. This is an early variety of good
quality, and is the kind most extensively grown
for early picking in the best hop districts. The
strobile is firm and compact, of medium length,
roundish in cross-section, and the stipular bracts
and bracteoles are broad and rounded at the
tip. The yield is moderate.
White's Marly. This and the Bramling are
the only early varieties of good quality. White's
Early is a superior kind, exceptionally early, but ^
usually a poor cropper : the ' petals ' are thinner hng Hop>
and paler than those of the Bramling, and the strobile not so
long. The tip of the strobile is generally open and loose.
B. Mid-Season or Main Crop Varieties
Rodmersham or Mercer's Hop ; CobVs Hop.
These are comparatively modern varieties of medium quality,
hardy and good croppers. They resemble the Canterbury White-
24
342 CANNABACE^E
bine hop in form and were derived from this variety. Both are
pale in colour with thin petals.
They are usually ready to pick after Bramlings and before the
Canterbury Whitebines.
Canterbury Whitebine ; Farnham Whitebine.
These two strains of hop, grown originally in the neighbour-
hood of Canterbury in Kent and around Farnham in Surrey
respectively, are apparently the same variety, no differences, so
far as botanical features are concerned, being noticeable.
They take the first place among hops for quality and also
yield good crops on deep rich soils. They are, however, some-
what delicate in constitution.
The * bine ' is pale green, often slightly mottled with red streaks.
The strobiles are medium-sized, roundish-oval in shape, with
smooth thinnish 'petals' which, when ripe, are a pale golden-
yellow colour.
The former variety has several names : it is grown on the best
hop ground in East Kent.
Tfo Golding. At the end of the i8th and beginning of the iQth
century a hop known as the Golding was largely grown. It was
stated by Marshall in 1798 to have been selected from the Canter-
bury Whitebine hop by a Mr Golding, living near Maidstone. The
true Golding hop is larger than the Canterbury Whitebine variety,
and grows more singly on the * laterals ' : its flavour and lupulin-
content are excellent. The bine is shorter than that of the
Canterbury Whitebine, and much more spotted with red.
At present the term Golding is often applied fraudulently to
many inferior varieties of hops.
Mathon or Mathon White. A variety originating or largely
grown first in the parish of Mathon, in Worcestershire. It ranks
practically equal in quality to the Canterbury Whitebine, which it
much resembles in form and colour of hop.
Cooper's White. An old Worcestershire variety very similar in
shape, colour, and texture of * petal ' to the White's Early of Kent.
It is less hardy than the Mathon. Both the above kinds
LATE VARIETIES 343
appear to be degenerating in constitution as the plants do not
last so long as formerly.
Fuggle's Hop. A modern variety raised about sixty years
ago, and now largely grown throughout the country on the stiffer
soils, where the best quality hops yield but a poor crop.
It produces an elongated pointed * hop ' of rather large size and
squarish in cross-section : the stipular bracts and bracteoies are
narrow, stiff, and somewhat pointed.
The crop is large but of medium quality.
C. Late Varieties
Bates' Brewer. A variety usually ripening after the Fuggle.
The strobiles are very compact, the bracts being arranged very
evenly and closely on the axis. Both the stipular bracts and
the bracteoies are broad and firm with well-rounded tips, and
resemble those of the Bramling variety in shape and texture.
It is one of the most distinct varieties of hops, and is con-
sidered of good or medium quality, although the flavour is
generally somewhat inferior. In most localities the crop is
generally small.
Grape Hops. There are several strains of grape hops many of
them having their strobiles closely placed on the branches in
dense clusters like grapes, hence the name.
The individual strobiles vary much in size in the different
strains, but all are pointed and somewhat triangular in outline.
In some of the examples we have examined the bracteoies are
broadish and roundish at the tip, but usually both the stipular
bracts and bracteoies are drawn out to a point at the tips and
partially resemble a Fuggle hop in these particulars.
The grape hops are a pale golden colour when ripe, but vary
much in quality, some of the smaller strains being classed as good,
while those producing larger strobiles are of medium quality only
Among the grape-varieties the best quality late hops are found.
Colgate. A very late variety, not much grown because of its
rank objectionable aroma. The strobiles are small and a pale
344 CANNABACE^C
yellow or greenish colour : they hang in dense clusters like those
of the grape varieties. The stipular bracts and bracteoles are
narrow and pointed.
Wild Hops.
Bus? Hops.
These two varieties are practically identical in shape and quality.
The strobiles are somewhat small, roundish-oval in shape, with
thin pointed stipular bracts and bracteoles ; when ripe the latter
are a pale whitish straw colour. The pale colour is very charac-
teristic of these varieties, and both are very poor in ' lupulin.'
It is worthy of mention that the wild hop here mentioned
is really a well-selected cultivated variety, and the seedlings often
met with wild in hedges are usually quite different from it in
form and size.
CLIMATE AND SOIL. Some of the roots of the hop plant descend
to great depths in search of water, and for the successful
cultivation of the choicest varieties a deep porous loam rich in
humus and containing a considerable proportion of lime is
needful.
When grown at all on the stiffer clay loams only the coarser
and less delicate varieties are planted : very stiff clays and dry
sands are, however, unsuited to the hop plant.
Hops of the best quality are generally grown in open situations
with a south sunny aspect, and where a free circulation of air
is met with : they must, however, be sheltered from cold or
violent winds.
PLANTING. Hops are propagated by ' sets ' or ' cuttings '
which are obtained as a by-product when the plants are ' cut '
or ' dressed ' in spring.
If the plants are allowed to grow freely, in a very few years
the rhizomes spread over too large an area for convenient
cultivation and training of the 'bines 1 : to prevent this and
keep them within bounds the soil round each plant is scraped
away in spring so as to expose the upper pans of the rhizome,
LATE VARIETIES
345
after which the thickened basal portions of each of the previous
year's ' bines ' are cut off within a quarter of an inch or less
of the old rhizome. The latter, therefore, extends but a short
distance each year, and the thickened pieces cut off are called
'cuts' and are either used for the formation of * sets' for the
propagation of the crop, or are thrown away.
Each ' cut ' is from 4 to 6 inches long and bears upon it two
or three opposite groups of buds (Fig. 108).
The 'cuts' are either planted out in the
garden at once, in which case they are known
as ' cut sets,' or are placed in beds in a nursery
until autumn, at which time they are removed
to their permanent quarters in the hop-garden :
the latter is the best and most usual practice,
and ' cuts ' treated in this way are known as
' bedded sets.'
The 'sets' are planted in rows, the rows
being from 6 to 10 feet apart, and the plants
from 5 to 8 feet apart from each other in the
rows. Usually they are planted at the corners
of squares of 6 or 7 feet side.
Hops may also be raised from ' seed ' (fruits)
sown in autumn. About half the plants ob-
tained in this manner are males and of no use
to the grower; the rest female plants are
generally of poor quality, and very rarely re-
semble the female parent. For example, most
of the female seedlings from the choice Canter-
or 'cutting/ a ]?iece of bury Whitebme variety yields strobiles which
d bine or
old dead 1
buds as at b.
| are coarse and of objectionable aroma. The
\ large preponderance of plants of very poor
quality among seedlings is no doubt connected
with the fact that one of the parents, namely, the male, is always
practically a wild form, for, on account of their being of no use
346 CANNABACE^E
to the grower, males have never been subject to special selection
and improvement.
It is somewhat curious that, although female seedlings show
considerable variation, we have never seen any morphological
differences among males, no matter what their origin, except in
one or two solitary instances where the fines' were a paler
colour than usual.
Raising from 'seed* is, however, the only way of obtaining
new and vigorous distinct varieties, but as the practice involves a
great deal of time, labour, and patience in the selection and
subsequent propagation of the plant, it is rarely attempted.
With one or two unimportant exceptions all the modern intro-
ductions have been casual selections of individual plants which
have shown some peculiarity different from their neighbours
in an ordinary hop garden.
YIELD, The hop crop is subject to very great fluctuation,
due to adverse climatic influences and the attack of parasitic
fungi and insects.
Cultivation and the application of manures also very largely
modify the yield. On some farms not more than five or six cwt.
of dry hops is obtained even in the best seasons, while on, others
a ton per acre is not uncommon.
The average crop in this country for the last ten years is about
8 cwt. of dry hops per acre.
COMPOSITION. The secretion contained in the 'lupuhV or
hop-glands is a complex mixture of several substances, the chief
of which are (a) hop-oil and () resins.
The hop-oil is an essential volatile oil, which gives the hop
strobile its characteristic aroma ; it appears to be secreted most
vigorously when the gland is young.
The different aroma of the* different varieties is no doubt due
to uninvestigated compounds present in the hop-oil.
Of the resins three varieties have been isolated. Two of
these, designated soft-resins, are intensely bitter, and communi-
LATE VARIETIES 347
cate their taste to beer; they also have antiseptic properties,
and are said to prevent the deleterious fermentative action of the
lactic acid and other bacteria inimical to the brewer's work,
without affecting the action of yeast and the acetic acid bacteria.
The third resin, possibly an oxidation product of hop-oil, is
pleasantly bitter, with little or no antiseptic power.
On keeping, the two soft resins lose their useful properties,
becoming changed into hard forms. Old hops/ therefore, are
of inferior value to the brewer.
The volatile oil present in hops varies from '2 to *8 per cent. :
the total resin-content is usually from 13 to 18 per cent.
Besides the secretion of the glands the bracts and bracteoles of
the hop strobilecontain within their cells various com pounds usually
met with in vegetable leaf-tissue. One of the substances present
is hop-tannin, which, with its nearly-allied phlobaphene, is no doubt
of service in the precipitation of albuminous material from beer
wort, although there is much difference of opinion on this point.
Ex. 174. Make observations on hop ' sets ' and cuts ' obtained when the
plants in a hop-garden are ' dressed ' in spring.
Note the thick basal portion of the ' bine ' which has borne * hops' last
season, and also the number and position of the buds upon it.
Split one of these ' cuttings ' longitudinally, and note how far the * bine *
has died back.
Ex. 175. Examine which way a hop ' bine ' twines round its support.
Observe the colour and roughness of the stem, and the shape and position
of the leaves upon it.
Ex. 176, Examine the structure of a full grown strobile or female inflor-
escence of a hop.
Note (i) the thickness and length of the ' strig ' or axis ; (2) the shape and
relative sire of the stipular bracts and bracteoles ; and (3) the presence
or absence of ripe fruit.
Which bracteoles are largest, those subtending fertile fruits or those sub-
tending abortive fruits.
Ex. 177. Carefully slit open a. ripe fruit and set free the embryo of the
teed ; examine the embryo for radicle and cotyledons.
Ex. 178. Examine young strobiles 'in burr.' Make sections of it, or
dissect so as to show the female flower and its parts, and the small stipulat
bracts and bracteoles.
348 CANNABACE^E
Carefully watch the strobile from day to day in order to understand the
change from ' burr f to ' hop.'
Ex. 179. Examine the flower and inflorescence of a male hop plant.
Ex. 180. On which part of the bracteoles of a strobile are the Mupulin*
glands situated? Are any present (i) on the axis of the strobile, (2) on its
stipular bacts, or (3) on the perianth of the female flowers?
Ex. 181. Examine the ' lupulin '-glands with a low-power microscope.
4. Hemp (Cannabis sativa L.). An annual dioecious plant in-
troduced to Europe from the East. It is cultivated for its tough
bast fibres, from which sail-cloths, sacking, and other coarse
textile materials are prepared.
Its fruits, popularly termed ' seeds, 1 are also used for feeding
small cage-birds and poultry. The seeds contain from 20 to
25 per cent, of a fatty oil, sometimes used as a substitute or
adulterant of linseed oil. The ' oilcake ' is utilised as a manure.
The stems of the plant, which produce many branches, are erect
and stiff, and usually grow to a height of 5 or 6 feet. The
bast fibres within are not so fine as those of flax, even when the
plants are grown thickly together.
The leaves are large and palmate, with from five to seven long
lanceolate serrated leaflets.
The male flowers have five-lobed perianths and five stamens ;
they resemble those of the hop, and are borne in loose panicled
inflorescences as in the latter plant. The female flowers are also
very similar in structure to those of the hop, and are produced
on separate plants usually of larger growth than those on which
male flowers are borne.
Sparsely scattered glandular hairs are met with on the leaves
and stems of the plant. In the hot climates of India, Syria, -and
elsewhere these glands secrete a volatile oil, and a resin which
has powerful narcotic properties ; in colder climates the secretion
is almost devoid of poisonous qualities, although the plant pos-
sesses a peculiar stupefying odour. Hemp * succumbs to a
moderate degree of frost, consequently when grown in this
HEMP 349
country for its fibre or its fruits, the 'seed* is not sown until
the beginning of May, after the disappearance of late spring
frosts.
When the seedlings are established they grow very rapidly,
but a satisfactory crop can only be obtained on deep rich loams
and alluvial soils containing a considerable amount of humus.
Ex. 182. Examine ordinary hemp ' seed ' ; note its form and colour ;
dissect out and examine the embryo of the seed within.
Ex. 183. Sow some hemp seeds in good garden soil, and make observa-
tions on the seedlings and full grown plants.
CHAPTER XXVI.
POLYGONACEJE.
i. Essential characters of the Order. Flowers small, usually
bisexual, with a regular perianth of three to six free segments.
Andrcecium perigynous or hypogynous, of five to eight stamens
opposite the perianth segments. Gyngecium superior, of two or
three united carpels, the ovary unilocular, usually triangular or
oval in section and containing a single erect basal orthotropous
ovule. Fruit an angular nut, usually more or less covered by
the persistent perianth.
Seed endospermous, the endosperm white and floury.
The Order includes about 750 species, most of which are
herbaceous perennials found in temperate regions.
The stems are frequently hollow with swollen nodes.
The leaves are alternate, simple with membranous connate
stipules which form a tubular sheath the ochrea embracing the
lower part of the inter nodes.
The roots are often astringent, due to the presence of tannic
and gallic acids, and in many plants the leaves contain con-
siderable amounts of oxalic acid or acid oxalates.
Important genera are Rheum (Rhubarbs), Rumex (Docks and
Sorrels), Fagopyrum (Buckwheats), and Pofygonum> a large genus
from which the Order takes its name.
2. The genus Polygonum has small, bisexual flowers in
racemes or spiked clusters.
The perianth is five-partite, stamens five to eight, styles two
or three, fruit a triangular or oval nut.
Two common annual weeds belonging to the genus are
850
COMMON BUCKWHEAT 351
Black-bindweed (P. Convolvulus L.) (p. 609) and Knot-grass
(P. aviculare L.) (p. 609).
3. The genus Ritmex has small unisexual or bisexual flowers,
generally arranged in long panided or racemed whorls.
The perianth is six-partite in two whorls, the three inner
segments enlarged when the fruit is formed; stamens six, in
pairs ; styles three, filliform ; the fruit a triangular shining nut,
enclosed by the enlarged inner segments of the perianth. Im-
portant weeds are the Docks (p. 608) and Sorrel (p. 618).
4. To the genus Fagopyrum belong two cultivated species,
viz. :
(1) Common Buckwheat (Fagopyrum sagittatum Gilib.).
(2) Tartarian Buckwheat (Fagopyrum tataricum Gaert).
The name Buckwheat means ' Beech '-wfieat, the ' seeds ' of
the plant resembling in miniature the seeds of the Beech tree,
the German name for which is * Buche/
(i) Common Buckwheat or Brank (Fagopyrum sagittatum
Gilib. = F. esculentum Moench. or Polygonum Fago-
pyrum L.).
Common Buckwheat appears to be derived from Fagopyrum
cymosum Meiss., a wild species found in India, Manchuria, and
the adjacent regions north of the latter country ; it was intro-
duced into Europe in the Middle Ages.
The plant is popularly included among grain crops, but it is
not a true cereal and in no way related to wheat.
Its 'seeds' yield a white flour used extensively in many
parts of Central and Eastern Europe, various countries of Asia,
and in North America, for human food. Though deficient in
gluten and unsuited for bread-making, the flour makes excellent
easily digested cakes and porridge. Buckwheat meal is also
useful, in moderate quantities, as food for horses, cattle and pigs,
and the whole grain is largely employed in the feeding of
poultry and game birds.
The green crop can be fed in small amounts to cattle and
352 POLYGONACE^E
sheep, although in larger quantity it is liable to produce vertigo
and other illness. Mixed with peas and vetches it may be used
as green food for dairy stock, equal parts of seed of the three
plants being sown broadcast.
Its chief use in a green state is for ploughing in as manure
before a wheat crop.
Bees are able to obtain considerable amount of honey from
the flowering crop.
ROOT. The root system consists of a tap root and numerous
short laterals, which do not spread far or deeply into the
ground.
STEM. The stem has few branches and is upright, from i to 3
feet high, hollow, angular, and more or less downy, with swollen
nodes.
LEAVES. The leaves are alternate, the upper ones almost
sessile, the lower ones with petioles up to 4 inches long ; the
blades are hastate or cordate triangular, acute, 2 to 4 inches
long, with hairs on the veins beneath. The stipules are short.
INFLORESCENCE AND FLOWERS. The inflorescences consist of
axillary and terminal cymes with more or less densely clustered
flowers.
The perianth is five-partite, usually pink or pinkish white, not
enlarged in fruit. The stamens are eight ; alternating with them
at their bases are a similar number of rounded yellow glands,
which secrete honey. The ovary is triangular, one-celled, and
contains a single erect ovule ; the style is tri-partite, each part
with a knob-like stigma.
The flowers are dimorphic. Some of the plants bear flowers,
the stamens of which are short and the styles about one-third
longer ; in others the stamens have long filaments which project
some distance above the stigmas of the short styles.
Pollination is chiefly carried on by bees and other insect
visitors, and crossing between the long and short-styled plants
is probably most frequent : pollination, however, between
COMMON BUCKWHEAT 353
flowers of the same structure as well as self-pollination are also
possible.
FRUIT. The fruit of the Common Buckwheat is a three-
angled ovate nut about 6 mm. long and 3 mm. broad, at the base
of which some of the dry perianth remains (Fig. io8a). The faces
FIG. io8a. t. Fruit or 'grain' of Common Buckwheat, a. Cross
section of i showing section of cotyledons (S-shape) surrounded by
endosperm. 3 Fruit of Tartarian Buckwheat. 4. Cross section of 3.
are glabrous, somewhat polished, generally slightly convex, and
the angles of the fruit more or less acutely keeled. The colour
is brown or grey marbled with darker spots and lines.
SEED. The seed has a pale brown testa and is triangular like
the fruit and free within it. The endosperm, which is white and
opaque, contains much starch in the form of round or polygonal
grains.
The embryo is embedded in the centre of the endosperm,
and possesses two thin, broad cotyledons which in transverse
sections of the fruit are seen folded in the form of an S.
(Fig/ ioa).
VARIETIES. There are several varieties of Common Buck-
wheat, differing chiefly in height, branching habit, and colour of
the stems, as well as in size and colour of the grain ; the chief of
these are :
(a) Common Buckwheat with brown or greyish brown fruits.
354 POLYGON ACE^
(b) Silver Grey Scotch or Silver Hull Buckwheat, a shorter,
somewhat more hardy, and more branched form with small ashy
grey fruits.
(c) Japanese Buckwheat, a tall, green-stemmed, late variety,
with large dark brown fruits, the angles of which are acute and
extended almost into the form qf wings. (For size and weight
of fruits, see p. 667).
CLIMATE AND SOIL. Buckwheat succeeds best in a mode-
rately cool, moist climate ; continued drought, especially when
the plant is in bloom, reduces the yield of seed. It is a delicate
plant, very easily damaged by two or three degrees of frost,
but on account of its rapid growth may be ^rown in countries
where the winter is severe if sowing is delayed until the early
summer.
It gives a useful yield on poor land, and is specially
adapted for growth on sandy loams and acid soils where few
other crops succeed ; on stiff clays it does not thrive. Heavy
doses of manure are detrimental, as they lead to the lodging of
the crop.
SOWING. When a crop of grain is the object, the seed is sown
at the end of May or early in June, after all likelihood of frost
is past, the most suitable temperature for germination being
about 60 F.
It may be sown broadcast, or in drills 12 to 15 inches apart, at
the rate of i bushel when drilled up to 3 bushels per acre when
broadcasting is adopted, the seed being covered by i to 2 inches
of soil. . For ploughing in as green manure the seed should
be broadcasted at the rate of 2 to 2^ bushels per acre in June or
July, the plants being turned in when they are beginning to
bloom.
HARVESTING AND YIELD. The seeds ripen very unevenly,
the upper parts of the inflorescence continuing to bloom after the
seed is ripe on the lower portions. The crop is ready for har-
vesting when the seeds on the lower part of the plant are ripe
COMMON BUCKWHEAT 355
at the end of August or early in September, 12 to 14 weeks after
sowing.
The average yield of grain is about 24 bushels, but under
favourable climatic conditions on good soils, a return of 40 to
50 bushels per acre is sometimes obtained.
Since many of the stems and leaves are still green, when the
crop is cut it is difficult to harvest except in seasons when there
is a succession of not less than 10 to 15 dry hot days, and as
the seeds shed easily careful handling is necessary.
COMPOSITION. The pericarp forms about 40 to 43 per cent,
and the true seed 57 to 60 per cent, of the fruit or 'grain.*
According to Wolff, Buckwheat ' grains ' have the following
composition : Water 13 to 14 per cent., carbohydrates 58 to 59
per cent,, proteins 10 per cent, and fibre 15 per cent. The
haulm is used for litter, and sometimes for fodder, but it is
coarse and of poor quality; it contains about 10 per cent, of
water, 4 per cent, proteins, 46 per cent, fibre, and 33 per cent,
carbohydrates.
(2) Tartarian Buckwheat (Fagopyrum tataricum Gaert).
Cultivated largely in India and other parts of Eastern Asia, as
well as in Europe and North America in lesser degree ; it is a
more hardy and coarser plant than Common Buckwheat, with
taller stems (2 to 3 feet high), which are usually green and less
branched. The leaves are similar in shape to those of Common
Buckwheat, but smaller.
The flowers are white, in small clusters. The fruit is ovoid,
conical with more or less wavy outline, brownish grey in colour,
with dull irregular faces, on each of which is a deep furrow ; the
angles of the fruit are rounded except near the tip, where they
are slightly keeled (Fig. io8a).
One variety of this species (var. himalaica Batalin) has small
grey dehiscent fruits, the seeds of which are exposed when
ripe.
CHAPTER XXVII.
CHENOPODIAOEJE,
i. General characters of the Order. Flowers small, regular ;
hypogynous, except in the genus Beta, which has epigynous
flowers. Perianth green, five partite, persistent Andrcecium
of five stamens opposite to the perianth segments. Gynaecium
with a one-celled ovary containing a single ovule. Fruit usually
a nut, more or less enclosed by the perianth, which is mem-
branous, fleshy or woody. Seed endospermous with a curved
embryo.
The plants of this Order are generally herbaceous, with simple,
entire exstipulate leaves. The latter are often fleshy, and in
some genera appear covered with a whitish powder or meal.
This appearance is due to short hairs which grow from the
epidermis, each hair consisting of a stalk of one or two cells,
terminated by a large round or star-shaped cell containing clear
watery cell-sap.
Most representatives of the Chenopodiaceae are met with near
the sea and on the shores and marshes surrounding inland salt
lakes.
Many weeds belonging to the Order are specially luxuriant
upon well-manured ground and on waste places where urine and
faecal matter have been deposited. The whole Order seems
specially adapted to exist in soils much impregnated with*
common salt, nitrates of sodium and potassium, and similar
compounds, and the application of common salt to the mangel
and beet crop usually improves the yield.
The genera belonging to it which need special mention are
356
SEA-BEET 357
Chenopodium (Goose-foot or Fat Hen), Atriplex (the Oraches),
and Beta (Beet and Mangel).
The genus Chenopodium includes a number of annual species
widely distributed on waste ground, and often prevalent as weeds
upon well-manured arable land. They are all very variable
plants and difficult to distinguish from each other. Perhaps
the commonest species is White Goose-foot or Fat Hen (C.
album L.) (see p. 608).
Good King Henry or All-good (C. Bonus-Henricus L.) is a
perennial species sometimes used instead of spinach as a pot-
herb, and frequently found on waste ground near villages.
The genus A triplex embraces a number of variable species,
most of which somewhat resemble the Goose-foot in outward
appearance. They are however monoecious (see p. 608).
To the genus Beta belong wild sea-beet, and the cultivated
garden and field beets.
2. Sea-Beet (Beta maritima L.) is a perennial plant common
on muddy sea shores. The root is tough, moderately thick, and
fleshy. The angular stems, which are many and branched, are
prostrate below, but their tips curve upwards to a height of
i or 2 feet. The lower leaves are smooth, about 3 or 4
inches long, fleshy, ovate-triangular, and the blade narrowed into
the broad petiole ; the upper ones smaller and lanceolate. The
inflorescence, flowers, and fruit resemble those of the mangel
described below.
3. A large number of cultivated forms of beet are known, some
of which are grown chiefly in gardens, and used as a vegetable
for human consumption, while others, such as mangels and
sugar-beet, are cultivated on the farm. They vary much in the
colour and sugar content of their so-called fleshy * roots, 1 and also
in their resistance to frost. The shape and amount of the ' root '
which appears above the soil is also subject to variation. All
the forms appear to be merely varieties of one species, which has
been named Common Beet (Beta vulgaris L.) They differ from
25
358
CHENOPODIACE^B
the wild sea-beet of our coasts (B. maritima L.) in being
biennial in habit and in having straighter upright flowering
stems, and a more well-defined uniform tap root. These
cultivated forms most probably originated from a variety grow-
ing wild on the western coasts of the Mediterranean and on
the Canary Isles, and known as B. vulgaris L., var. maritima
Koch. Whether this plant is really distinct, or is itself a variety
of Beta maritima L., is not certain.
Of the garden forms little can here be said. Their roots are
mostly of conical or napiform shape, with deep crimson tender
0)
FIG. 109. i. Mangel 'seed' (fruit) germinating, a Primary roots
from two separate^embryos.
2. True seed separated from x.
3. Longitudinal section of 2. a Root ; b cotyledons ; c hypocotyl ;
x endosperm.
flesh, which is rich in sugar. A variety known as Chard Beet
(B. vulgaris L., var. Cicla L.) is sometimes cultivated for the
broad pale fleshy midribs of its leaves, which are cooked and
eaten like sea-kale.
4. Mangel Wurzel or Field Beet. Mangel Wurzel is the Ger-
man for 'Root of Scarcity] by which phrase this plant was
known about the time of its introduction into England as a
field crop about 100 years ago.
This appellation appears to have arisen from the fact that
it often produces a great crop when other plants fail. It
MANGEL WURZEL OR FIELD BEET 359
equally deserves the name from the fact that it keeps well until
late spring and early summer, when turnips and swedes have
been consumed and grass and other forage crops are scarce.
SEED AND GERMINATION. The parts known in commerce as
mangel * seeds' are in reality fruits, two or three of which are
often joined together. Each fruit contains a single endosper-
mous seed.
FIG. no. 4, Seedling mangel; 5 and 6. Older examples of the same, a Root; coty-
ledons ; c hypocotyl ; d first foliage-leaves of plumule.
The seed is kidney- shaped, about the size of a turnip seed,
with a dark smooth testa. Just within the latter lies the
embryo, which is curved round the central endosperm. Dur-
ing germination the cotyledons absorb the endosperm and
remain within the seed-coat some time after the root has made
36o
CHENOPODIACE^E
its exit (3, Fig. 109). Eventually the cotyledons become free from
the seed and appear above ground. The young plant possesses
two narrow cotyledons, a well-marked hypocotyl, and a primary
root, which is quite distinct from the latter (4, Fig. no).
ROOTS AND HYPOCOTYL. The primary root is well-developed,
and secondary roots arise upon it in two longitudinal rows
(6, Fig. no). The total root-system is very extensive and often
penetrates to great depths in suitable
soil. It is not infrequent to find drains
4 and 5 feet below the surface of the soil
blocked by them. In the subsequent
growth of the plant the hypocotyl be-
comes pulled more or less into the ground
by the contraction of the roots, but the
hypocotyl and root always remain more
or less distinct ; the former rarely bears
any adventitious roots.
The ' mangel ' of the farm, which is
generally termed a 'root,' consists of
thickened hypocotyl and true root; the
relative proportion of each part is not
however, the same in all varieties. In
the long-red and ox-horn varieties the
hypocotyl grows out of the ground; in
others, such as the sugar-beet, the hypo-
cotyl is shorter and pulled beneath the
surface of the soil.
A collection of leaves is seen at the
apex of the mangel, and just below them R * c : Ti^
are the remains of the old leaf-bases, whcre cot y ledon was present
which give to this part a rough rugged appearance (Fig. 114).
A transverse section (Fig. 112) shows a series of concentric
rings of firm vascular tissue alternating with rings of soft thin-
walled parenchymateus bast; the cell-sap of the parenchyma,
MANGEL WURZEL OR FIELD BEET 361
midway between the vascular rings, often has a crimson or yellow
tint. In white-fleshed varieties the cell-sap is clear, and these
parenchymatous zones are translucent when thin slices are held
up to the light. The vascular rings consist of isolated strands
or groups of vessels with thin-walled parenchymatous medullary
rays between.
It is outside the scope of the present work to deal with the
complex growth in thickness of the root and hypocotyl of the
mangel ; but it may be mentioned that each ring of vascular
strands, with the medullary rays between and the corresponding
zone of thin- walled bast, is the
product of a separate cambium
tissue.
The individual cambium-rings
arise in the pericyle of the root in
rapid regular succession from the
centre outwards.
Sooner or later the cell-division
of the inner ones ceases, but the
exact length of time during which
r
FIG. us. i Transverse section of mangel 4 root. 1
2. Longitudinal sect ion. ^ r Lateral roots ; a ring of vascular bundles ; b thin-walled
parenchyma (chiefly bait-tissue).
each cambium-ring remains active is not certain. In ordinary
varieties usually six or seven cambium-rings complete their
362 CHENOPODIACE/E
growth in the six months during which the mangel is growing
in this country.
Sometimes it is assumed that mangels with yellowish zones of
parenchyma, such as is present in the Golden Tankard variety, are
richer than those with quite white flesh. This, however, is an
error, as very frequently white-fleshed varieties, e.g. most sugar-
beets, are much richer than those with yellow or crimson flesh.
There appears to be no direct connection between the colour of
the ' flesh ' and sugar-content.
The .sugar is not evenly distributed in the tissues of the
mangel, the rough * neck ' contains much less than the rest of the
' root.' Moreover, the greatest amount of sugar is present in the
cell-sap of the parenchyma lying close to the vascular ring, the cells
in the middle of the zone of parenchyma between two successive
rings of vascular tissue being comparatively poor in this sub-
stance. The richest mangels are therefore those in which the
vascular rings are most closely placed together, and in which the
parenchyma, poor in sugar, is consequently reduced to a minimum.
For 'roots ' of the same diameter the best kind are those which
have the greatest number of vascular rings.
INFLORESCENCE. During the first year the mangel usually
stores up reserve-food in its hypocotyl and root, and the stem
above the cotyledons remains short and bears a number of leaves
in a close rosette.
In the following year the terminal bud and axillary buds of
this very short stem send up strong leafy angular stems which
rise to a height of 3 feet or more, and these and their branches
terminate in inflorescences.
The inflorescence consists of an elongated axis upon which at
short intervals the flowers are arranged in dense sessile clusters,
each containing from two to seven flowers (A, Fig 113) ; below
each cluster is a small bract.
THE FLOWER (B> Fig. 113) is epigynous and about \ of an
inch in diameter. It is bisexual and possesses a small green
MANGEL WURZEL OR FIELD BEET 363
five-leaved perianth, the lower part of which is united with the
fleshy receptacle. The androecium consists of five stamens
opposite to the perianth.
The ovary of the gynaectlim is
sunk partially in the fleshy
receptacle and contains a single
ovule (C, Fig. 113).
The flowers of the mangel and
beet are protandrous, and flowers
' set ' no fruit if specially isolated
or prevented from receiving pollen
from neighbouring flowers. Cross-
pollination appears to be effected
by the agency of small insects and
the wind.
THE FRUIT. After fertilisation
the fleshy receptacle and base of
mon of the inflores- the perianth of each flower enlarge
c Toneo P Tn an a g n e done closed flower of considerably and the separate
mang , e , l< . , e a ^ I flowers in each cluster become
C, Vertical section of a flower, o Ovule.
z>, Cluster of two fruits developed from m ore or less firmly united with
flowers of B. Such clusters constitute /
commercial mangel 'seeds.' each Other (Z>, Fig. 113). The
fleshy parts with the imbedded ovaries eventually turn hard and
woody, and the clusters of spurious fruits finally fall off or are
thrashed off the long axis of the inflorescence and come into
the market as ' seeds.'
The latter are in reality collections of two or more spurious
fruits. Each spurious fruit consists of the hardened receptacle
and perianth with the ripened gynaecium containing a single
seed, and as several of these fruits may be present in each
commercial c seed ' it will be readily understood that when one
of the latter is sown several seedlings may spring from it.
This peculiarity necessitates the separate hand thinning of a
young crop of mangels, otherwise by growing so closely together
364 CHENOPODIACE^
the seedlings injure each other and produce deformed and
small * roots/
The true seed is very small, a fact which must be taken into
consideration when sowing is contemplated as it is readily buried
too deeply for proper germination.
VARIETIES. Mangels may be conveniently divided according
to their shape and the colour of the skin of the parts below
ground. Usually the petiole and main veins of the leaves
resemble the skin of the ' root ' in tint, and there is frequently a
tendency for the parenchymatous zones or soft rings of the flesh
to be similarly coloured.
Much variation, however, exists in the colour of the skin and
flesh, few crops proving quite ' true ' in these respects. The best
varieties, especially the Golden Tankard, are most subject to
reversion, and need constant attention on the part of the seeds-
man to keep the strain ' true.'
A good mangel should yield a heavy crop, and the feeding
quality should be as great as possible. Besides these points it
is of importance to note the depth to which it grows in the soil,
as the expense of lifting a deeply-seated crop may materially
reduce its usefulness from the farmer's point of view.
It must, however, be borne in mind that, so far as composi-
tion is concerned, mangels with ' roots ' below the ground are
richer in sugar and of better feeding-value than those with
* roots ' above ground.
The continuation of the tap root should be single and small ;
those with * fanged/ thick secondary roots are more difficult to
pull and clean, and generally of a coarse and fibrous nature. The
' neck ' or rough upper part of the mangel should be as small as
possible, and its flesh firm and solid, with no tendency to spongi-
ness in the centre.
The variety should be as ' true ' as possible, so far as its shape
and colour of skin is concerned, and its keeping qualities should
be good.
OX-HORN VARIETIES
A common fault with some strains is their inclination to ' bolt '
or behave as annuals, and produce an inflorescence the first
season without forming a thickened ' root.'
Long Varieties. In these the c roots ' are three or four times
as long as they are broad (A, Fig. 114), and are generally about
FIG. 114. Chief forms of mangel 'roots.' A, Long. , Inter-
mediate. C, Tankard. D t Globe.
a half or two-thirds above the soil. These varieties give the
greatest yield per acre of any kind of mangel, and are suited to
deep soils, especially clays and loams. They are divided into
(i) long red and (2) long yellow varieties, according as the skin
is red or yellow.
The long yellow kinds are somewhat superior in quality to the
long red ones, but both are coarse and fibrous, and of lower
feeding value than most of the varieties mentioned below.
Ox-horn Varieties. These are very closely allied to the
long red and long yellow varieties, but their * roots ' assume
a twisted horn-like shape. The part below ground does not
descend below the depth of the plough furrow : they are therefore
suited to shallower soils; but their irregular growth makes it
366 CHENOPODIACE^E
difficult or impossible to cultivate between the rows. The quality
is not good, but the yield is large.
Intermediate or ' Gatepost ' Varieties. These have large
oval roots (2?, Fig. 1 1 4), somewhat intermediate between the long
and globe varieties. They may be either red, yellow, or orange
in colour of skin, and are suited to comparatively shallow soils.
Tankard Varieties. The typical shape of these resembles
C, Fig. 114. Two kinds are grown, namely, Golden Tankard, with
orange coloured skin, and flesh with yellow zones ; and Crimson
Tankard, in which the skin is crimson or rose colour, and the
flesh with crimson rings.
All tankard varieties have small ' roots/ and give small crops,
unless grown somewhat closely in the rows.
The nutritious quality of the Golden Tankard, however, sur-
passes that of all other varieties of mangel
Globe Varieties. In these the * roots * are spherical or nearly
so, and by far the larger part of each grows above ground
(Z>, Fig. 1 14). They are especially suited to the light and shallower
classes of soils, where they may be made to produce an excel-
lent crop, which is readily lifted or pulled from the soil. Per-
haps the commonest form is the Yellow Globe, the nutritive
value of which ranks second to the Golden Tankard. Red and
orange varieties are also grown.
CLIMATE AND SOIL. The mangel requires a warm, dry
climate, that of the south of England being much more suited
to its growth than the north. The most satisfactory soils are
deep clays and loams, especially for the long varieties, but
lighter soils, except those of loose sandy character, produce good
crops of Globes and Tankards.
SOWING. The ' seed ' is generally sown between the middle
of April and the beginning of May in drills 27 inches apart
for the Globe and Tankard, and 2 1 to 24 inches apart for the
longer varieties. It requires a somewhat high temperature to
germinate satisfactorily, and it should not be drilled at a greater
GLOBE VARIETIES 367
depth than f of an inch below the surface, for, although the so-
called ' seed ' is of some considerable size, the true seed is small,
and has little power to make its way upward if buried too deeply.
The amount of ' seed ' used is from 6 to 8 Ibs. per acre. The
young plants are subsequently * singled' so as to leave from 10
to 14 inches between each plant in the row, the smaller distances
being adapted for the long varieties, especially if smaller and
relatively more nutritious ' roots ' are desired.
YIELD. The average yield of ' roots' per acre is about 18 to
25 tons.
COMPOSITION. Cane-sugar is one of the chief ingredients in
the mangel. The amount varies from 3 or 4 per cent, in the
large long red varieties to about 7 or 8 per cent, in the Golden
Tankard and well-grown Globes.
The water-content varies from 86 per cent, in the best kinds to
92 in the poorer varieties. Usually they are much superior in
composition to turnips, but in damp, cold seasons large roots
may be as watery as white turnips.
Mangels cannot be fed to stock immediately after being re-
moved from the land in autumn, as they contain some ingredient
which produces ' scouring ' in animals ; what the substance is
which is responsible for this effect is not clear ; possibly it is
a nitrate or oxalate. Nitrates are present in considerable
abundance in autumn, but these compounds gradually diminish
in amount if the mangels are kept till spring. The injurious
substance, whatever it is, disappears to a large extent on keeping,
the yellow-skinned varieties are generally ready to feed to stock
before the red ones.
The nitrogenous substances in mangels average about 1*2 per
cent, of which a little less than half are albuminoids. Several
distinct amides are generally present, especially when the
4 roots * are not ripe. The fibre averages about "9 per cent.
5. Sugar-Beet. The name sugar-beet is given to selected varie-
ties of mangel which are specially grown for their sugar<ontent
368
CHENOPODIACE^E
The mangel first selected for improvement was a White
Silesian variety (Fig. 115, A\ which may be considered as the
parent of all the chief varieties now grown.
Sugar-beets are comparatively small, the best weighing about
i J to 2 \ Ibs., and of conical or elongated pear shape. Unlike the
ordinary mangels the sugar-beets have their thickened 'roots 1
entirely buried in the soil, those with large ' necks ' above
ground being less valuable in many ways and poorer in sugar.
FIG. 115. Chief forms of sugar-beet.
A, White Silesian Beet or Mangel.
P, Knauer's Imperial and Klein-Wanzlebener.
C t Vilmorin's Improved.
The * roots ' should not be ' fanged,' and in good varieties
the skin is white, and the flesh firm and white, with a large
number of close concentric rings of vascular bundles. Beets
with upright leaves and long petioles are always less rich in sugar
than those with leaves which lie close to the ground and have
shorter petioles.
The chief forms are exhibited in the varieties mentioned
below :
Vilmorin's Improved. The ' root ' is conical in shape (Fig.
SUGAR-BEET 369
115, Q, and the leaves spread out as a flattish rosette on the
ground when ripe.
Knauerti Imperial (Fig. 115, .#).- A pear-shaped variety,
usually with white flesh sometimes inclined to a roseate hue.
The leaves, which have reddish veins, grow more upright than in
the former variety and have somewhat crenated and puckered
margins.
Klein-Wanzlebener. A variety resembling the preceding one
but with more spindle-shaped root and green leaves.
CLIMATE AND SOIL. Sugar-beet thrives best in a climate
possessing a warm and moderately damp summer, and having
somewhat dry, hot months of August and September, during
which time the sugar is stored in the root in greatest abundance.
Climates such as are met with in Southern Europe are too dry
and the North is too wet for satisfactory sugar production by
sugar-beet. In wet climates the roots are poor in sugar.
Average seasons in the British Isles are probably too damp
for successful cultivation of this crop, although fair yields of
roots with good sugar-content have been grown for experi-
mental purposes during the last two or three somewhat dry
seasons.
The soil most suited to the crop is a medium loam of good
depth containing a considerable proportion of lime.
Heavy wet clays or very dry sandy soils are not suitable. If
farmyard dung is used as manure it is essential that it should
be ploughed in during autumn or applied to a previous crop.
The quality of. the roots is much influenced by a good supply
of potash salts especially the carbonate; phosphates are also
beneficial and the yield is increased by an application of nitrate
of soda or ammonium sulphate applied in the early stages of
growth of the plant.
SOWING. The seed is drilled or dibbled in rows about 14 or
15 inches apart and the plants are subsequently singled by hand
when about a quarter of an inch thick, so as to stand 6 to 8
370 CHENOPODIACE./B
inches asunder in the row. As the young plants are very
susceptible to frost the seed should not be sown before about
the middle of April or the beginning of May. The amount
of seed necessary to drill an acre is about 30 Ibs. : it is usually
soaked in water for 24 hours before sowing, and should not be
buried more than an inch deep.
HARVESTING. The vegetative period necessary for the satis-
factory production of a 'ripe* root is from 140 to 150 days in
England, so that if sown at the proper time the crop is usually
ready to be harvested from about the middle to the end of
September, at which time the roots are dug up with a narrow
spade or a two-pronged fork.
YIELD. The yield is usually from 12 to 16 tons per acre.
COMPOSITION. The water-content of a sugar beet is about
82 per cent. The amount of cane sugar present averages 15
or 16 per cent, in good varieties; the woody fibre about 1.3
per cent.
Ex. 184. Germinate some mangel 'seeds* in damp sand. Find out how
the root escapes from the fruit.
Carefully extract some of the true seeds with a strong needle or a knife,
and cut sections to show the curved cotyledons and endosperm.
Ex. 185. Examine seedling mangel plants in various stages of development,
paying special attention to the primary root, hypocotyl, and secondary roots.
Ex. 186. Cut transverse and longitudinal sections of a full grown mangel
'root. 1 Note the distribution of the vascular tissue and soft parenchyma.
Observe which parts are coloured pink, crimson, or yellow, and which are
white.
Ex. 187. Cut transverse sections and count the 'rings* in large and
small mangel * roots ' from the same crop. Note if the difference in total
diameter of the ' roots ' is due to greater width of each ring or to a greater
number of rings in the larger specimens.
Ex. 188. Examine and describe the stem, leaves, and flower of a * bolted *
mangel or a normal second year plant.
Ex. 189. Examine a number of commercial mangel ' seeds.' Observe the
shrivelled tips of the perianths, and find out the number of true fruits in each
so-called 'seed.'
Ex. 190. The student should become acquainted with the chief character!
of the common species of Chtnopodium and A triplex.
CHAPTER XXVIII.
CRUCIFERJE.
i. General characters of the Order. Flowers (Fig. 116, A),
regular, hypogynous. Calyx polysepalous, four sepals in two
t t whorls, deciduous; corolla
^ polypetalous, four petals in
one whorl : andrcecium of six
stamens in two whorls, tetra-
dynamouS) that is, four sta-
mens with long filaments, and
two with short ones. (Fig.
1 1 6, B\ Gynsecium (Fig.
FIG. 116. A, Flower of turnip. ^5,The.same,
after stripping off the calyx and corolla,
^ f\ cvnrnrnnn*; twn rnr
, O > C / SyncarpOUS, tWO Car
showing the androecium and gynaecium. s Two pe l s . the OVUleS are arranged
short stamens; / four long stamens; st stigma *
of gynatcium; n nectary. C, Gynaecium. o Its O n tWO parietal placentas J the
ovary ; b style; st stigma. f f
ovary is sometimes unilocular,
but more frequently divided into two compartments by a * false '
partition, which is an outgrowth from the placentas.
Fruit, usually a dehiscent silique or silicula (see Raphanus, p.
392), seeds without endosperm or with only traces of it. When
placed in water the cuticle of the testa of the seeds from the
dehiscent fruits generally swells up into a slimy sticky substance,
which fixes the seed to the ground, tends to store up water dur-
ing germination, and also aids in the distribution of the seeds.
Situated on the receptacle, generally at the base of each of the
two short stamens, are greenish nectaries.
Pollination is chiefly brought about by insects. The anthers
are so placed in regard to the stigmas and nectaries, that insects
871
372 CRUCIFER^C
frequently effect cross-fertilisation when searching for honey. Self-
fertilisation is however common, and productive of good seed.
The Order comprises about 1200 species, mostly of herbaceous
or slightly shrubby character ; practically all are non-poisonous
and extensively represented in temperate and cold regions.
The inflorescences are usually simple racemes without bracts
or bracteoles.
Many plants belonging to the Cruciferae, such as cabbage, kohl-
rabi, turnip, swede, rape, and white mustard, are very valuable
to the farmer.
Acrid, pungent compounds are present in various parts of
mustard, charlock, radish, and many other cruciferous plants.
Instead of starch being stored as reserve food-material for
the young plants, the tissues of the embryos of nearly all the
Cruciferae contain considerable quantities of oil.
The seeds of several species belonging to the genus Brassica
furnish oil which is sold under the name of Colza oil or Rape oil.
A number of plants, such as charlock, wild radish, shepherd's-
purse, Jack-by-the-hedge, and hedge mustard, belonging to the
order are common weeds of the farm, while others, such as
the wallflower, stock, and candy-tuft, are ornamental plants
of the garden.
So far as the fanner is concerned, the most important genus
of the Cruciferae is the genus Brassica, which includes the turnip,
swede, rape, and the cabbage and its varieties : some botanists
include black mustard, white mustard, and charlock in it, while
others place these plants in a separate genus, Sinapis: the
former plan is adopted here.
2. Wild Cabbage (Brassica oleracea L.). This plant, which is
the parent of all the cultivated forms, grows on the sea cliffs in
the south of England and various pans of northern Europe.
It is a biennial, or perennial with a stout erect stem from i to a
feet high. The lower large, broad leaves, are obovate with
lobed margins, smooth, and of ashy green hue. The upper
CULTIVATED CABBAGE 373
leaves are smaller and sessile. The flowers are pale yellow,
often an inch in diameter, arranged in long racemes.
The siliques are smooth, about 2 or 3 inches long, and stand
out from the main axis of the inflorescence.
3. Cultivated Cabbage, and its varieties (Brassica oleracta L.).
Few plants have given rise to so many fixed varieties or races
as the cabbage. Almost every part of its structure, except the
root and seeds, has been modified by man for his own use.
The seeds of all the varieties are so similar that they cannot
be distinguished from each other with certainty (p. 647). The
young seedlings also present great similarity, and have two
notched cotyledons, similar to those of the turnip in Fig. 117 j
the first foliage-leaves are quite smooth and of glaucous tint
In all the forms of cultivated cabbage the inflorescence,
flowers, fruit, and seeds are similar to those of the wild cabbage
mentioned above : it is in the growth of the vegetative parts
and the young inflorescences that the most striking variations
are seen.
All the cultivated forms are biennial and fall into several groups,
namely :
i. Brassica olcracea L., form accphala.
The terminal and axillary buds of the varieties in this group
grow out into leafy shoots in the first season, and therefore give
rise to an elongated stem and branches bearing a considerable
number of green foliage-leaves for which these plants are grown.
These varieties most nearly resemble the wild cabbage : repre-
sentatives are the Borecoles, especially Scotch kail, and Thousand-
headed-kail.
ii. Brassica oleracea L., form gemmifcra.
This form resembles the preceding one in possessing an erect
elongated stem, but the axillary buds upon it, instead of
branching out immediately, become more or less compact and
round. The plant is grown for these buds, which are usually
about i or 2 inches in diameter. The chief representative
is the Brussels Sprout. g
374 CRUCIFER^E
iii. Brassica okracea L., form capitata.
In this group the stem remains short and the terminal bud
develops into a very large 'head* of closely overlapping smooth
leaves. The so-called ' white' and 'red 1 (really green and
purple) Drumhead cabbages are examples.
iv. Brassica okracea L., form subauda or bullata.
This name is applied to what are known as Savoy cabbages.
They are similar in structure to the capitata forms, but have
puckered or wrinkled leaves.
v. Brassica okracea L., form gongy lodes or caulo-rapa.
In this form the stems above the cotyledons remain short and
become very thick and fleshy. It is known as Kohl-rabi of
turnip-rooted cabbage.
vi. Brassica okracea L., form botrytis.
In this group the axis of the inflorescence and all its many
branches are formed during the first year's growth, and become
thickened and fleshy when young. The hardy forms are known
as Broccoli, those more tender and liable to injury by frost are
spoken of as cauliflowers.
Many of the varieties of cabbage are only grown in gardens.
A few, however, are useful crops of the farm ; the chief ones
grown as food for stock are Thousand-headed kail, Drumhead
and Savoy cabbages, and Kohl-rabi.
4. Thousand-headed kail This form of Brassica okracea
grows to a height'of 3 or 4 feet, sending out leafy branches all
along the strong woody stem, and these again branch until an
extraordinarily large amount of succulent forage is produced.
The leaves are dark green, with wavy, slightly crinkled margins.
Thousand-headed kail is very hardy and rarely suffers from
even prolonged frosts. It is chiefly used as food for ewes and
lambs in autumn and spring and generally consumed on the
field where it is grown.
5. Cabbage. The word cabbage is generally applied to all those
varieties the leaves of whose terminal buds form a compact
375
round or oval head. They differ considerably in rapidity of
growth, and may be classified into early and late varieties
Some of the early varieties reach maturity of 'head' in the
early autumn of the same year in which they are sown, while
the late varieties during the same period of growth are but half
grown and comparatively immature.
They may also be classified according to the shape into (i)
Drumheads with flattened spherical 'heads,' which take up
lateral space and require to be planted some considerable
distance apart ; and (ii) Ox-hearts which have oval or bluntish
cone-shaped 'heads.' The latter varieties take up less space
and may be planted nearer together than the Drumheads.
The cabbages are fairly hardy, but the 'heads' contain a
considerable amount of water (generally 89 per cent.), and do
not stand wet weather or frost so well as the open Thousand-
headed variety. Cabbages are largely grown for feeding dairy
cattle and sheep, and are more nutritious than white turnips.
They increase the flow of milk and in moderation are less liable
to give a taint to it than turnips, especially if the outermost
leaves are discarded.
Savoy cabbages are more hardy than those with smooth leaves,
and are therefore more adapted for winter use than the latter
varieties.
6. Kohl-rabi is a form of cabbage with a thickened turnip-like
stem which stands quite above the ground although in good
strains, often close to it.
The fleshy part is developed from the stem above the
cotyledons, none of the hypocotyl or root being present in it :
it thus differs from the turnip, mangel and carrot.
As Kohl-rabi suffers very little in the driest weather it is
sometimes designated 'the bulb of dry summers.' It re-
sembles the swede turnip in feeding-quality and yield, but
stands frost better. The leaves as well as the stem are useful
food for stock.
376 CRUCIFEIUE
The varieties differ in the shape of the thickened stem, some
being almost spherical while others are oval.
They vary also in colour, some being glaucous green and others
a purplish tint.
Both early and late varieties are known.
CLIMATE AND SOIL. All the varieties of cabbage produced on
a farm are capable of growing in climates which are much too
dry for the proper development of the turnip. They are also
better adapted for growth on strong loams and clays than the
latter plant.
SOWING. In many cases the cabbage and its varieties are
drilled or sown broadcast in small prepared seed-beds, upon
sheltered ground. The young plants are subsequently trans-
planted out in the field when 6 or 8 inches high.
Most of the crops may, however, be drilled in rows in the
field where they are to grow, the superabundant plants being
thinned out and the remainder left to develop.
The seed may be sown at varying intervals of time in
such a manner as to provide a succession of green food almost
throughout the whole year. Usually in those cases where the
crop is to be used during the autumn and early winter, the seeds
are sown in beds in February, March and April, the young plants
transplanted in June and July, and the crop ready for consumption
from September to December. When drilled on the field where
they are to grow June and July are the months for sowing, the
crops being utilised from September to December.
Seeds of the hardier varieties may be sown in beds in August,
the young plants transplanted in October and November, and the
crop will be ready for consumption in the following spring and
summer.
The seeds may also be drilled in August and September to
produce a crop during the following spring and summer.
The rows of plants vary from 20 to 30 inches apart, according
to the variety grown, and other circumstances.
TURNIP
377
Usually the plants are equidistant from each other, both in the
row and from row to row.
The amount of seed when the plants are raised in a seed-bed
is i Ib. for each acre to be subsequently planted ; if drilled on
the field direct 4 or 5 Ibs. per acre are necessary.
YIELD. An average crop of cabbages is about 30 tons, that
of Kohl-rabi about 20 tons per acre.
FIG. 117. A, Seedling of turnip (Brasst'ca Rata L.). T Root ; h hypocotyl;
c cotyledon; p first foliage-leaf ('rough leaf 1 ). , Seedling of charlock
(Brassica Sinapis Vis.).
COMPOSITION. Kohl-rabi is richer in albuminoids and * fibre*
and poorer in carbohydrates than swedes, ^he average water-
content is about 88, the digestible carbohydrates about 7, fibre
1*5, and albuminoids 2*3 per cent, respectively.
7. Turnip (Brassica Rapa L.). This name is applied to a
378
CRUCIFERyE
biennial plant grown extensively for its thick fleshy so-called
'roots/ which are produced during the first season of growth
and used as late summer, autumn and winter food for various
kinds of stock.
SEED AND GERMINATION. The seed is almost round, with a
reddish purple testa, and contains an embryo which resembles
that of white mustard in general form (Fig. 5). The seedling
possesses two smooth notched cotyledons and a hypocotyl and
root very distinct from each other. The first foliage-leaves are
FIG. 118. i. Longitudinal section of a turnip 'root.' 2. Transverse Tection of the
same, d Bast and secondary cortex; c cambium-ring ; a, degenerate wood, forming
main mass of the root ; r normal secondary root, originally produced when the primary
root was thin (almost all above this point is thickened hypocotyl) ; b old leaf-scars.
grass-green in colour, roundish with irregularly serrate margins and
their surfaces have scattered hispid hairs upon them.
ROOT AND HYPOCOTYL. A single tap root generally exists
from which a number of thin secondary roots arise. The total
root-system, although fairly extensive, does not descend to any
great depth, but spreads horizontally in the upper layers of the soil.
During the first year, both the hypocotyl and primary root
increase in length and thickness, the combined thickened
TURNIP
part, in popular parlance, being variously termed the 'turnip/
turnip 'bulb' or turnip 'root.' In all cases the amount of
bypocotyl is considerable, but the relative proportion of this
part of the plant to the true root is not the same in all varieties,
smd probably varies with the soil and cultivation which the plants
receive.
The swollen fleshy ' root ' of a turnip possesses essentially the
same arrangement of tissues as is common in ordinary roots
and stems. The relative proportion and composition of each
tissue is, however, very different.
A transverse section (2, Fig. 118) of a turnip 'root* shows an
outer layer about J of an inch thick, chiefly bast (d) ; within is
the wood (a) which forms the main mass of the ' turnip ' ; it is
produced by the cambium (c). Almost the whole of the wood
consists of thin-walled, unlignified wood-parenchyma, imbedded
in which appear radial lines of vessels in small isolated groups.
Medullary rays are present, but these are not readily dis-
tinguished from the degenerate wood-parenchyma: they form
but a comparatively small part of the fleshy ' root.'
LEAVES The stem upon which the leaves grow remains very
short during the first year : the leaves consequently appear in a
rosette-like bunch at the top of the so-called bulb. The first
foliage leaves are roundish with irregularly serrate margins, those
growing later being pinnatifid or pinnate with a large oval
terminal lobe (lyrate). All produced during the first year's
growth are grass-green and beset with rough harsh hairs.
In the second season the terminal bud in the centre of the
rosette of radical leaves, develops into a strong erect stem with
many branches. The leaves upon the latter are somewhat
glaucous and smooth, the upper ones being ovate-lanceolate,
sessile, with bases which partially clasp round the stem.
The ends of the branches and main stem terminate in
inflorescences.
* INFLORESCENCE AND FLOWERS. The turnip inflorescence is a
CRUCIFER^E
raceme which when young resembles a corymb, the open flowers
equalling or overtopping the buds which appears crowded
together. As the flowers open, the axis of the inflorescence
elongates, and the flowers then become separated from each
other by longer intervals. The flowers are small, about an
T
FIG. 119. Chief forms of turnip 'roots.' i. Long. 2. Tankard or spindle-shape. 3.
Round or globe. 4. Flat variety. 5. A typical bad 'root,' many-necked 'top 1 and fang-
like roots.
inch in diameter, of the ordinary cruciate type (Fig. 121), with
almost erect calyces and yellow corollas.
FRUIT. The fruit is a smooth elongated silique with a short
seedless beak.
VARIETIES. Turnips may be classified according to their shape
into the following groups.
TURNIP 381
i. Long varieties in which the fleshy 'root 'is three or more
times as long as it is broad (i, Fig. 119).
ii. Tankard or Spindle-shaped varieties (2, Fig. 119), in which
the greatest diameter of the * root ' is between * top ' and * tail.'
iii. Round or Globe varieties in which the ' roots ' are almost
spherical (3, Fig. 119).
iv. Flat varieties in which the shortest diameter is between
'top* and 'tail' (4, Fig. 119).
Many intermediate forms are prevalent, but the above repre-
sent the chief most distinct groups, so far as shape is concerned.
Turnips may be also placed in groups according to the colour
of the upper part of the ' root/ which is exposed to the light
and air above ground and the colour of the ' flesh. 1
A. White-fleshed varieties.
These have white flesh and bright canary-yellow flowers.
They are generally of low feeding value, many of them with
soft flesh, liable to be injured by frost.
Their growth is rapid, and a considerable amount of produce
is yielded in a short time. They are chiefly adapted for feeding
in autumn and early winter, and are conveniently divided into
(i) 'white tops/ (2) * green tops/ (3) 'purple or red tops/
and (4) ' greystones/ according to the colour of the upper part
of the * root' The greystone variety has its upper part mottled
with transverse green and purple streaks.
2?. Yellow-fleshed varieties.
These have firm reddish-yellow flesh and flowers of a reddish-
yellow tint. The leaves are rough and grass-green in colour.
These varieties are more robust, of slower growth, and superior
feeding value to the white-fleshed turnips ; they are, moreover,
less injured by frost and keep sound for a longer period during
winter.
Yellow-fleshed varieties are conveniently divided into (i)
' yellow tops/ (2) ' green tops/ and (3) ' purple tops/ according
to the colour of the upper part of the ' root.'
These plants are sometimes erroneously described as
1 hybrid turnips/ the pale reddish-yellow flesh suggesting a cross
between the white-fleshed turnip and swede. Hybrids of the
two latter plants have indeed been produced . but they are,
however, unlike the yellow-fleshed turnip and sterile.
8. Swede Turnips (Brassica Napo-brassica D.C. and Brassua
Rutabaga D.C.).
382 CRUCIFER^E
These plants are grown for the same purpose as the turnip.
They differ from the latter, however, in the following points :
(1) The first foliage-leaves of the seedling swede are rough
like those of the turnip, but glaucous in colour, never grass-green.
The leaves developed later are smooth and glaucous.
(2) The swede has a distinct short stem or 'neck* on the
upper part of the thickened ' root ' with well-
marked leaf-scars upon it (Fig. 120).
(3) The 'roots' are rarely so perfect in
form and outline as those of the turnip ; but
they keep much better during winter, and are
easily stored for use in spring.
(4) The seeds are usually larger and of
darker colour than those of the turnip,
Swede turnips may be divided like the
common turnips into two groups, namely :
(a) White - fleshed and () Yellow - fleshed
varieties. The white-fleshed forms (B. Napo-
brassica D.C.) have firm white-fleshed 4 roots'
FIG. no. Swede turnip pf irregular form and rough green skin ; they
gS'ed* ck rind' CM- * very hardy but rarely grown in this country,
pare with Fig. n 9 . xhe flowers of these varieties are a bright
canary colour like those of white-fleshed turnips but larger.
The yellow-fleshed swedes (B. Rutabaga D.C.) are the forms
most commonly cultivated ; they have solid yellow-fleshed roots
turbinate or oval in shape, with comparatively smooth skin,
which may be (i) green, (2) purple, or (3) bronze a mixture of
purple and green. The flowers are of buff yellow or pale
orange tint.
CLIMATE AND SOIL. For perfect development, both common
turnips and swede turnips require a somewhat damp, dull
climate, the north of England producing much finer crops than
the south. Where the air is dry the yield of * roots ' is small.
The best soils for their growth are open loams, the common
turnips being grown on the lighter kinds, swedes upon the stiffer
loams. Neither of them can be grown very satisfactorily upon
stiff wet clays, nor on dry sands or gravels.
SOWING. Turnips are drilled in rows on ridges where the
rainfall is considerable, and on the flat in warm, dry climates.
The distance between rows varies from 1 8 to 25 in. for white and yellow
turnips, and 20 to 27 in. for swedes.
SWEDE TURNIP 383
Common turnips being of more rapid growth are usually sown
later than swede turnips.
The sowing of the main crop of swede turnips usually takes
place from the middle to the end of May in the north ; the yellow-
fleshed turnips are sown somewhat later, and the white turnips
last of all, namely, from June ist to 2oth. In the south of Eng-
land these crops are sown about a month later than in the north.
The amount of seed used is from 2 to 3^ Ibs. per acre ; the plants
are singled so as to stand from n to 13 inches apart in the rows.
For feeding early in autumn small areas are often sown earlier
than the dates mentioned above.
Turnips may also be sown in August in order to provide green
leafy succulent food for sheep in spring.
YIELD. The average crop of white turnips weighs from 20 to
25 tons, yellow-fleshed turnips about 20 tons, and swedes from
15 to 20 tons per acre.
COMPOSITION. White turnips usually contain from 91 to 93 per
cent, of water ; swedes about 89 per cent. ; although in well-grown
crops of the latter the water -content is often as low as 87 per cent.
A great deal of variation exists ; even * roots ' growing near to-
gether in the same field sometimes vary widely in water-content,
and the particular variety, or ' strain ' of seed, manuring, width of
row, soil, climate, and ripeness, all influence the composition.
The amount of soluble carbohydrates, most of which is sugar,
averages about 5^ per cent, in well-matured white turnips and a
little over 7 per cent, in swedes. The fat-content is usually the
same in both, namely, *2 per cent., the albuminoids in white
turnips average '5 per cent., in swedes about 7 per cent ; the
fibre '7 and *8 per cent, respectively.
'Roots' of large size almost invariably contain more water,
and are therefore poorer in dry matter than smaller ones.
The difference is most marked in white-fleshed turnips, but
swedes, and we may say all ' roots/ exhibit similar variation in
composition.
384 CRUCIFER^
It is instructive to note that in two ' root ' crops whose water-
content is 87 and 92 per cent, respectively, every hundred Ibs.
of the former contains 13 Ibs. of dry substance, while too Ibs.
of the latter yield 8 Ibs. of solid substance when completely
dried : in other words, 20 tons of the former are equal in dry
weight to more than 32 tons of the latter. Differences in
water-content similar to these ordinarily exist between average
crops of swedes and white turnips, and even the same varia-
tions in composition have been met with in two swede crops,
one composed of somewhat small well-matured 'roots/ the
other consisting of very large immature 'show roots.'
As the turnip 'root' matures the percentage of water in it
decreases, and the percentage of carbohydrates, principally
sugars, increases.
The dry substance of the ' root ' also alters in composition as
the ripening proceeds; in unripe roots much of the nitrogen
exists in the form of amides, compounds which are of little
nutrient value, whereas in mature roots the amides have largely
disappeared, being transformed into useful albuminoids,
9. A good turnip. The following points are important in
determining the value of a turnip or swede.
(1) The yield should be high.
(2) The feeding-quality, so far as composition is concerned,
should be good ; roots of high specific gravity are generally more
valuable in this respect than those of low specific gravity.
(3) Their resistance to frost is to be considered. It is to
some extent dependent on inherent vital differences, and also to
the manner of growth of the ' root ' ; varieties which grow mainly
buried in the soil are usually more resistant to frost than those
whose ' roots ' are mainly above the surface of the soil.
(4) Varieties which stand well out of the ground are however
more easily pulled up and more readily and completely consumed
by sheep than those deeply buried.
(5) Turnips should have no 'neck' and that of the swede
RAPE, COLE, COLESEED 385
should be thin. The 'skins' of the fleshy 'root* should be
as thin, smooth, and tender as possible. Both the tap root
and leafy top should be single and small. Turnips or swedes
with several tops and fang-like roots, as in 5, Fig. 119, are
generally of poor feeding-quality, and involve much waste in
their consumption.
The upper part of the ' root ' should be convex ; when con-
cave, as partially seen in 4, Fig. 119, rain-water is liable to be
held in the depression and decay thereby encouraged.
10. Rape, Cole, Coleseed (Brassica Napus L.). This plant is
a biennial, grown in many places instead of a turnip crop, and as
a ' catch crop ' for its succulent leaves and stems which are
utilised as food for sheep.
The seeds are dark purple or black, and the young plants
have glaucous foliage-leaves which are sparsely covered with
rough hairs. Both seeds and seedlings are identical in appear-
ance with those of swede turnips, and not unfrequently rape seed
has been sown in mistake for that of the swede, and the young
plants hoed out as for a root crop ; in such instances it is
impossible to detect the error until the plants have grown
some time, when the want of * bulbing* propensity betrays
them.
The root is slender ; the stem which grows to a height of 2
feet or more is smooth, with many branches. The lower leaves
are lyrate, the upper ones ovate-lanceolate, clasping the stem.
The flowers are bright yellow, like those of the white-fleshed
swede.
Seed is sown at intervals, usually from May onward, in order
to provide a succession of crops during the autumn and winter.
It is generally sufficiently advanced in three months from the
time of sowing to provide a large bulk of green food.
The seed is sown broadcast, at the rate of 10 Ibs. per acre, or
more frequently drilled at the rate of 4 or 5 pounds per acre.
In the latter case, the superabundant young plants are hoed out
386 CRUCIFER^
and the remainder left a little nearer together than the ' roots '
of a white turnip crop.
The green rape crop usually contains about 86 per cent, of
water, 4 per cent, digestible carbohydrates, and 2 per cent, of
albuminoids.
The seeds are very rich in oil, usually averaging about 42 per
cent, of this constituent.
n. Oil- Yielding Rapes. On the Continent several forms of
plants belonging to the genus Brassica are grown for their seeds,
from which oil is expressed or extracted, and the refuse sold
as ' rape cake.' In this country the oil is sold indiscriminately
as colza oil or rape oil.
One of these oil-yielding plants greatly resembles the swede
except in its roots, which are not fleshy. Its flowers are bright
yellow. This is the same plant as that grown in this country
chiefly as a green fodder crop, and known as rape, cole, or
coleseed. The winter variety, of which there are several named
strains, is sown usually in August, and the seed harvested in the
following June and July. This variety gives the largest yield
of the best oil. There is also a summer variety of the same
plant which is sown in April and harvested in September of the
same year : it is not quite so rich in oil, and gives a poorer yield
than the winter one.
Besides the above, an oil-yielding plant is grown which
resembles the turnip, except in its want of a thick fleshy * root.'
The oil from its seeds is sold as rape or colza oil. There are
also winter and summer varieties of this * rape/ the first sown
in August and September, and the second in May. They differ
from the previously mentioned rape in ripening earlier. More-
over, they are smaller plants, give a smaller yield of oil, and are
more suited to sandy soils ; they are also hardier than the
swede-like rape. None of these forms of turnip-like 'rape 1
are grown in this country.
12. The nomenclature and relationship of these forms of
BLACK, BROWN, OR RED MUSTARD 387
Brassica to each other is not clear, as hybrids and crosses are
frequent. Possibly all are derived from one species : some
authorities are, however, disposed to notice two species with
varieties, thus :
Species i. Brassica campestris L.
Oil-yielding summer variety : form anntia. (a) Summer turnip -like Rape.
Do. winter do. : form oleifera. (/>) Winter do. do
Variety with thick fleshy ' root ' form rapifera
Species 2. Brassica Napus L.
Oil-yielding summer variety : form annua. (a) Summer Swede-like Rape.
Do. winter do. : form olctfera (b) Winter do. do.
Variety with thick fleshy ' root ' : form rapifera : Swede Turnip :
B. Napo-brassica D.C. i. white-fleshed.
B. Rutabaga I) C ii- yellow- do.
13. Black, Brown, or Red Mustard (Brassica nigra Koch. =
Sinapis nigra L.). An annual plant grown for its seeds. The
latter are ground and the * flour/ after removal of the dark-
coloured testas, is used as a condiment, namely, ordinary table
mustard.
The seeds contain oil which is sometimes extracted and used
for burning in lamps, in the same manner as rape or colza
oil.
The plant is a wild indigenous plant in this country, but most
frequently met with under hedges and in waste places as an
escape from cultivation. The seeds have the property of re-
maining in the ground for several years without germinating,
and when a crop is once allowed to seed, some of the shed seed
is certain to give rise to plants in many of the subsequent crops
grown on the same land. It may thus become a troublesome
pest of arable land.
SEED AND GERMINATION, The seeds are oval with a
reddish-brown coloured testa when well harvested, and the
3 88 CRUCIFEIUE
seedling resembles that of a turnip plant with somewhat small
cotyledons.
STEM AND LEAVES. The stem grows to a height of 2 or 3
feet, and is branched and covered with rough hairs. The lower
leaves are large and rough, lyrate, and of a light green colour :
the upper leaves lanceolate and smooth.
INFLORESCENCE, FLOWER, AND FRUIT. The inflorescence is a
long raceme ; the flowers are small, about J to an inch across,
have spreading narrow sepals and pale yellow petals, the broad
parts of which are slightly notched.
The fruit, which grows upright, and closely adpressed to the
stem, is a somewhat short smooth silique about to f of an inch
long with a short slender beak (5, Fig. 123); each valve of the
silique has a single strong well-marked longitudinal nerve. When
ripe the pods and seeds are of dark colour, hence the name
Black Mustard.
The whole plant resembles charlock, but can readily be dis-
tinguished from the latter by the length, shape, position and
nerves of its siliques.
Black mustard requires for its growth a deep, rich, fertile soil,
on which it is generally sown broadcast, at the end of March
or beginning of April. It is hoed and thinned in May and then
left until September, when it is cut rather green and allowed to
ripen in small carefully made stacks.
COMPOSITION. The seeds of black mustard contain about 25
per cent, of a fixed oil, which is sometimes extracted from the
* dressings ' obtained in the manufacture of table mustard, and
used for adulterating or mixing with rape and other oils. The
seeds when ground and mixed with water give rise to a some-
what volatile product known as ' mustard oil ' ; the latter does
not, however, exist ready formed in the seed, but is produced
by the action of an enzyme, myrosin^ upon a glucoside known
as sinigrm or potassium myronate, both of which are present
in the seeds. In the presence of water the my rosin decomposes
WHITE MUSTARD 389
the potassium myronate, splitting it 'into potassium hydrogen
sulphate, sugar and allylthiocarbimid or ' mustard oil. 9
The decomposition may be represented thus :
C 10 H 18 KNS,0 IO - KHS0 4 + C^O, + C 3 H 5 NCS.
Potassium myronate. Potassium hydrogen Sugar. ' Mustard oil*
sulphate.
1 Mustard oil ' has an extremely pungent taste and smell ; it
gives off vapour, small quantities of which bring tears to the
eyes ; when the oil is applied to the skin, it immediately pro-
duces blisters.
14. White Mustard (Brassica alba Bobs. * Stnapts alba L.).
An annual plant grown chiefly as food for sheep in this
country, and for ploughing in as a green manure to enrich the
ground in humus. Its seeds are also used for the manufacture
of oil, and for the preparation of table mustard as in the last
species. Young seedlings are used as a salad with cress.
Some botanists consider white mustard not a true native of
the British Isles.
When grown for seed it does not occasion any trouble as a
weed in subsequent crops after the manner of black mustard, as
its seeds all germinate at once when conditions are favourable,
and the young plants are then readily destroyed.
SEED AND GERMINATION. The seeds are much larger than
those of black mustard and pale yellow.
The seedling has notched cotyledons, and its first foliage-leaves
are pinnatifid or pfnnately lobed, as in Fig. 5, thus differing
from turnip and black mustard.
STEM AND LEAVES. The stem grows from i to 3 feet high,
and is generally branched and covered with rough hairs.
All the leaves are bright green and rough; they are lyrate-
pinnatifid or pinnate, with irregular lobes. The terminal lobe of
the leaf is usually small compared with those of the leaves of
turnip and black mustard.
27
390 CRUCIFER^E
INFLORESCENCE, FLOWER AND FRUIT. The inflorescence is
a long raceme, the flowers small, about \ an inch across,
with narrow spreading sepals and pale yellow petals. The fruit
is a hispid silique, about ij or 2 inches long, with a long,
slightly curved sword-shaped beak; the valves of the silique
have three nerves.
When ripe the siliques and seeds are of pale colour, hence
the name white mustard in contrast to the black species with
dark-coloured siliques and seeds.
Its leaves and siliques at once distinguish it from the other
species of Brassica mentioned.
For sheep-feed it is usually sown broadcast any time from
April to August, at the rate of 20 Ibs. of seed per acre. Its
chief merit is its very rapid growth, which makes it of service for
catch-cropping after vetches, potatoes, and other similar crops,
or where turnips have failed and the time for sowing a more
useful crop has past. It is ready for folding with sheep from six
to eight weeks after the seed is sown. For use as 'green
manure ' it is generally sown in July or August and ploughed in
during October and November.
COMPOSITION. The green plant in full bloom contains on an
average about 83 per cent, of water, 7^ per cent, of carbohydrates,
2 per cent, albuminoids, and 6 per cent fibre.
The seeds contain 26^ per cent, of a fixed oil similar to that
in other cruciferous seeds ; when extracted it is used for mixing
with rape oil.
The seeds of white mustard when ground and stirred with
cold water, have not the odour so characteristic of the black
species ; nevertheless the pungent taste is very similar in both
species.
A glucoside, which is named sinalbin, is present in the seeds
of white mustard, and the enzyme my rosin. When water is
added to both, the myrosin decomposes, the sinalbm into jiucose,
an acid salt of sinapin, and sinalbin mubtard oil (CyH 7 O'NCS).
CHARLOCK 391
The latter is somewhat less pungent than allyl mustard oil
obtained from black mustard seeds and is not volatile at
ordinary temperatures.
15. Charlock (Brassica Sinapis Vis. = Sinapis arvensis L).
A native annual unfortunately often too common in corn
fields.
SEED AND GERMINATION. The seeds are dark brown similar
in size to those of turnip, from which they cannot be readily dis-
tinguished when the two are mixed. When sown they germinate
irregularly and often remain capable of growth for several years
when deeply buried in the soil.
The seeds contain a considerable amount of oil and are sold
by many farmers to oil-cake manufacturers, finally appearing
as impurities in rape and other * cakes.'
The seedling is somewhat like that of a turnip, but can be
distinguished from the latter by the first foliage-leaves, which
are a darker green colour and of longer and somewhat different
shape (B, Fig. 117). It is more pungent in taste than a seedling
turnip.
STEM AND LEAVES. The stem is rough from i to 2 feet high
and branched. The lower leaves are stalked, ovate, partially
lyrate or lobed, the upper ones lanceolate, irregularly serrate,
and sessile.
INFLORESCENCE, FLOWER AND FRUIT. The inflorescence is
a raceme. The flowers are larger than those of black mustard,
being generally J to j of an inch across ; they possess spreading
narrow sepals, and pale yellow petals.
The fruit is a silique from i to 2 inches long, usually with
rough deflexed hairs upon it, but occasionally smooth ; the valves
of the silique have three faint veins (2, Fig. 123).
The whole plant resembles that of black mustard, but has
larger flowers and differently shaped siliques, which latter are
spreading and not pressed to the stem.
392
CRUCIFER^E
1 6. TABLE OF THE CHIEF DISTINCTIONS BETWEEN THE
COMMON SPECIES OF BRASSICA.
A. Sepals erect or nearly so (Fig. 121).
i. Leaves of 1st year's plant glaucous (ashy grey).
a. All leaves smooth, flowers pale lemon
yellow. Cabbage.
b. First leaves of seedling with a few
stiff hairs, flowers buff, or pale
yellow. Swede and swede-like
'Rape.'
FIG. Ji.-Flower " Le aves of 1st year's plant grass-green
of cabbage, showing with Stiff hairs, flowers bright yellow, of charlock, showing
erect sepals, s. Turnlp and tumip.jiHe Rape. spreading sepals, *
FIG. 122. Flower
B. Sepals spreading (Fig. 122).
i. Siliques erect, closely pressed to main axis on which they grow :
valve of silique with one nerve. Black Mustard.
ii. Siliques spreading, valve of silique with three nerves.
a. Silique with sword -like 'beak/ seeds pale yellow or straw-
colour. White Mustard.
b. Silique with cylindrical straight
beak, seeds dark -brown. Char-
lock.
17. Wild Radish: Jointed Charlock
(jRaphanus Raphanistrum L.). An
annual weed common and troublesome
in cornfields in many districts although
unknown in others.
The stems are from i to 2 feet
high and covered with scattered rough
FIG. 123. Siiiquesof: i. Turnip hairs. The leaves are rough, coarsely
(Brassica Rata L.). 2. Char- , . , . , . , ,.
lock (Brassica Smafis vis.), serrate, and simply lyrate (with few
3. White Mustard (Brassica . ., . . .
alba Boiss.). 4 . wild Radish pmnatifid segments and a large ter-
minal lobe). It has racemose in-
florescences. The flowers are about
f of an inch across with erect sepals, and usually pale straw-
coloured petals often veined with purple lines ; occasionally the
petals are white or pale lilac tint.
(RagJtanus Raphanistrum L.).
5. Black Mustard (Brassica
ttifra Koch.).
WILD RADISH: JOINTED CHARLOCK 393
The siliques, which are from i to 3 inches long, have
long slender beaks and are constricted above and below each
seed (4, Fig. 123) ; they are indehiscent, but separate at the
* joints 1 into barrel-shaped pieces, each containing a single
seed.
The seeds are oval and reddish-brown in colour.
The whole plant somewhat resembles ordinary Charlock, but
may be distinguished from the latter by its erect sepals, usually
veined petals, and smooth 'jointed' siliques.
Ex. 191. Examine seeds of cabbage, swede and turnip in bulk, and indi-
vidually with a lens. Compare them with seeds of black mustard and
charlock. Taste all of them separately in the above order and note any
differences in flavour.
Ex. 192. Grow seedlings of cabbage, swede turnip, black mustard, white
mustard, and charlock. Note the shape of the cotyledons and first leaves of
each.
Ex. 193. Compare the external appearance of a full grown swede with that
of a white turnip.
Ex. 194. Carefully examine and describe the leaves, flowers and fruits of
the crucifers mentioned in detail in the text, and draw up a table of differ-
ences, paying special attention to the calyx, the colour and form of the
corolla, and the form of the siliques.
Ex. 195. Watch the growth of the fleshy 'root* of a turnip or swede.
Find out which part is hypocotyl and which true root. Make marks with
Indian ink, & of an inch apart, on the hypocotyl of young seedlings, and
note their position from day to day.
Ex. 196. Make careful observation on the development of a kohl-rabi
plant from the young seedling stage up to the time when the stem is 2
inches thick. Find out whether the part of the stem above or below the
cotyledons thickens most.
Ex. 197. Growbrussels sprouts, savoys, broccoli, and thousand-headed kail
side by side and watch their development : make notes of the differences in
length of stem and the development of the buds in the axils of the leaves
upon it, in each kind of plant.
Ex. 198. Examine the various forms of cabbage when the inflorescences
are well developed and their flowers open.
Are the flowers of the different forms alike in all respects ?
Ex. 199. Compare and contrast longitudinal and transverse sections of a
turnip, a carrot and a mangel respectively.
394 CRUCIFER/E
Ex. 200. Procure a small amount of seed of each of the chief kinds of
turnips and swedes from various seedsmen. Sow short rows of each on the
farm in order to become acquainted with the form and colours of the root,
and the hardness and colour of the flesh. Note the differences in the
size of the neck and tap root, and the amount of * root ' above and below
ground.
Ex. 201. Sow a few seeds of rape or cole and swede side by side in differ-
ent rows or in different pots of earth and compare the seedlings before and
after the foliage- leaves appear. How soon does the swede show that it
differs from the rape plant ?
Ex. 202. Grind up the seeds of black mustard and mix with water : do
the same with those of white mustard. Smell and taste both.
Ex. 203. The student should become acquainted with such common
cmcifers as shepherd's-purse, Jack-by-the-hedge. and hedge mustard,
CHAPTER XXIX.
LINAGES.
i. General Characters of the Order. Herbs, shrubs, or trees.
Leaves simple, entire, generally alternate and exstipulate, or
with small stipules only.
Flowers regular, hypogynous. Calyx, inferior, four or five
sepals, persistent. Corolla polypetalous, four or five petals
twisted or imbricate in the bud, soon falling.
Andrcecium of four or five perfect stamens, often alternating
with a similar number of teeth or abortive stamens, all united
to a hypogynous ring.
Gynaecium, syncarpous, three to five carpels, the ovary having
three to five loculi, each of which is sometimes partially divided
by a false dissepiment,
One or two pendulous ovules in each loculus.
Fruit, a roundish capsule, splitting along the dissepi-
ments.
Seeds eight or ten in each fruit, with a small amount of endo-
sperm and a straight embryo.
The Linaceae comprises a small Order of about 150
species.
The genus Linum includes about ninety species, some of which
are cultivated in gardens on account of their brilliantly coloured
flowers. The most important species belonging to the Order is
Flax or Linseed (Linum usitatissimum L.).
2. Flax or Linseed (Linum usitatissimum L.). Flax has been
grown from time immemorial for the manufacture of linen, a
895
396 LINAGES
fabric which is woven from the bast fibres of the stem of the
plant.
The plant is also grown for its seeds, which contain a large
quantity of oil. The latter is extracted and sold under the name
of linseed oil, the crushed seed after extraction of most of its oil
being made up into oilcake and utilised by the farmer for feeding
stock.
The original unextracted seed is sometimes employed as food
for calves and other animals, and the fibre of the stem, in addition
to its being used in the manufacture of linen, is also made into
a tough and very durable paper.
SEED AND SEEDLING. The seeds are oval and flattened, about
4 to 6 mm. long, of a yellowish brown colour and possessing a
smooth shining surface. The epidermis of the coat of the seed
is formed of cubical cells with very thick walls, consisting of a
peculiar mucilaginous substance, which swells up into a slimy
mass when put in water.
Within the seed coat is a small amount of endosperm and a
large straight embryo. Germination takes place readily when
fresh seed is sown, and the young plant sends its two elliptical
cotyledons above ground.
ROOT. The root-system of the plant is comparatively small,
consisting of a weak tap-root and a few short lateral roots, none
of which penetrate deeply into the soil.
STEM. The stem is slender, and when the plants are
grown closely together for the production of good fibre, rises
to a height of i to 2 feet without branching, except in its
upper part.
The internal arrangement of the structural elements is
seen in Fig. I23A, where a portion of a transverse section
of the stem is given. On the outside is a well-marked
epidermis, beneath which comes the cortex, consisting of
parenchymatous cells, some of which contain chloroplastids.
Next is observed an interrupted ring of bast fibres, arranged
FLAX OR LINSEED
397
C
in larger or smaller bundles. Some of the larger bundles have
from twenty to thirty fibres in each, and are very strong.
In a full-grown stem each fibre has a very thick cell-wall and
small cell-cavity: it is
pointed at each end, and
varies in length from 4 to
66 mm.
The fibrous bast strands
or 'flax' when isolated
are a pale yellowish tint
in the best kinds of plants,
and possess a silky lustre.
When flax fibre is the
object for which the plant
is grown the stems are
carefully pulled by hand
before the seed is ripe,
and laid on the ground
for about a day, during
which time they dry a
little.
The following day the FIG. i2 3 A.-Tran S vcrsc section of portion of a Flax
ef/ame ar<* firrl intr\ email stem, a, epidermis; 6, cortex; <r, bast fibres
stems are tied into small ( , flax . } . ^ wood or xylem of the stenu
straight sheaves, 4 to 8
inches in diameter, and the latter are then set up in stooks
to dry more completely. In eight or ten days the plants
are 'rippled,' that is, the seed capsules are removed by
pulling the stems between the teeth of iron combs. The
capsules are afterwards threshed and the seed is either kept
for sowing, or, if unripe, utilised by the oil-crusher. After
cutting off the roots, the stems are subjected to the process of
* retting ' or rotting, the object of which is to loosen the tissues
of the stem so that the bast fibres can be easily freed from
the cortex, wood, and other parts of the stem.
398 LINAGES
Various methods of 'retting* are practised in 'different dis-
tricts, one of the oldest and best being that adopted in the
Courtrai district of Belgium.
The dry flax stems are there kept from the time of harvest-
ing in one season until the middle of April or later in the
following year. They are then tied into bundles and sunk
in crates in the River Lys. After remaining under water
seven or eight days the bundles are taken out and arranged
in small stacks to dry.
When dry they are sunk a second time for ten or twelve days,
and after being removed from the river and dried again, the
* retting ' is complete.
During this process the middle lamella between the
adjoining cells of the tissues forming the stem becomes more
or less completely dissolved, and the component cells are
loosened from each other. The middle lamella, according
to Mangin, consists of calcium pectate, and its solution is
brought about by the fermentative activity of two or three
kinds of bacteria, most of which are anaerobic (see p. 785) or
nearly so, carrying on their work best in the presence of a small
amount of oxygen only, under conditions which obtain below
water. These organisms are most active at a temperature of
1 8 to 20 C.
After the retting is completed the dried flax stems are sub-
jected to the processes of ' breaking ' and ' scutching ' in order
to separate the brittle epidermal and woody parts from the more
elastic tough fibres.
LEAVES. The leaves are small, linear-lanceolate in shape,
with smooth surfaces, and arranged alternately on the
stems.
INFLORESCENCE AND FLOWERS. The upper part of the
single stems are branched in a corymbose manner, and
the flowers are borne on these branches in many-flowered
cymes.
FLAX OR LINSEED
399
The sepals are five in number, ovate, pointed and ciliate.
The polypetalous corolla is twisted when in bud and consists of
five blue or white delicate thin petals, which readily fall after a
few days ; these are connected to a hypogynous ring or disk on
which are five glands probably representing abortive stamens
opposite to the petals.
The flower possesses five stamens, and on the ovary are
five long styles. The ovary is five-celled, the cells being
1 2 3 4
FIG. 1238. -i Flower and pottion of stem of Flax (Linutn usitatissimunt L.)-
2. Gynaecium and androecium. 3. Transverse section of ovary. 4. Ripe
capsule.
divided into two by spurious dissepiments, in each of which
is a single ovule (Fig. 1238).
THE FRUIT is a capsule (Fig. 1233), which splits longitudinally
when ripe and sets free the ten seeds within.
VARIETIES. The typical form of Linum ttsitatissimum L.,
grown for flax production, is an annual with an upright solitary
stem and capsules which remain closed when ripe : the
partitions in the capsules are smooth. A variety (L. humiU
400 LINAGES
Miller = Z. crtpitans Boning.), grown in some countries for
oil seeds, has dwarfer, more branched stems and larger cap-
sules, which open and set free their seeds when ripe ; the
dissepiments are hairy.
CLIMATE AND SOIL. Flax succeeds best in a moderately
damp and warm climate. The soil most adapted for its growth
is a deep, well-drained, sandy loam, although it can be cultivated
upon a variety of soils, so long as they are not too dry and are
free from stagnant water.
On stiff clays, peaty soils, or soil containing much lime, flax
produces fibre poor in quality.
SOWING. As young flax plants are very easily destroyed by a
sharp frost, the seed should not be sown until all likelihood of
damage in this manner is past.
The middle of April is soon enough for most districts in
which the crop is grown ; but it is sometimes sown as early
as March or as late as May. The earlier the better, for
early seeding not only increases the yield and quality of the
fibre, but there is also more time left for the drying and
other processes connected with the preparation of the stem
before * retting'; the ground is shaded early in the season,
and the moisture in the soil thereby preserved from loss by
evaporation.
The amount of seed to be used for sowing varies according as
the crop is to be grown for fibre alone, for fibre and unripe seed,
or for seed only.
When the crop is cultivated for its fibre, or chiefly for the
fibre with a certain amount of partially ripened seed, the plants
should stand closely together, so as to induce the production of
long thin unbranched stems ; a thick seeding is therefore needed,
and the amount in such cases should be not less than 3 bushels
of seed, or about 160 to 170 Ibs. per acre.
If a crop of ripe seed is desired, the plants should have plenty
of room for healthy development, and from 70 to 100 Ibs. of
FLAX OR LINSEED 401
seed per acre is enough, the smaller amount being used when
the seed is drilled in rows 5 or 6 inches apart, the latter when it
is broadcasted by hand.
The seed saved from a partially-ripened crop of flax
grown mainly for the fibre, should be used for oil extraction
and oilcake manufacture, and not for sowing for another fibre
crop.
The best yield of flax, so far as fibre is concerned, is said by
some to be obtained from seed which has been carefully dried
and kept in tightly closed barrels which exclude moisture for two
or three years, experiments having shown that seed stored in this
way gives longer stems and finer bast than fresh seed ; others
consider that the highest yield of fibre is secured from the fully
ripened seed, harvested from a crop raised from * barrel' flax
seed.
Flax seed is readily damaged by heating, especially when
damp, and is liable to lose its germinating power very quickly
unless care is exercised in its storage. It should have a ger-
mination capacity of 90 per cent, at least, and should be sown at
a uniform depth on a clean, well-prepared seed bed.
HARVESTING AND YIELD. The crop is harvested in different
ways, according to the kind of produce required. Where the
finest white silky flax is the object, the plants are pulled up soon
after the fall of the petals of the flowers, at which time the stems
are still green in the upper parts, although the lower half is
yellow and has lost its leaves. The seeds in the young capsules
are then whitish in colour. Where both seed for oil-crushing
and flax are wanted, the crop is taken when the stem and cap-
sules have turned yellow, the seeds being then brown and well
formed. The flax produced is greater in bulk but is coarser
in texture, and does not become so white when bleached as in
the case of plants harvested earlier.
Where only seed for sowing is needed, it is essential that the
plants be allowed to stand until dead ripe.
402 LINAGES
The yield of raw flax, that is, the dry stems after the retting
process, varies from | to i tons per acre. About 80 per cent,
of this is removed in the breaking and scutching processes,
about 20 per cent. (;'.<?. 3 to 6 cwt.) remaining as fine scutched
flax.
The seed obtained from a crop grown for fibre should not be
more than about 4 cwt. per acre ; when the crop is grown for
seed only, the amount produced varies from 8 to 1 1 cwt. per acre.
COMPOSITION. The seeds from the ripe capsule contain from
31 to 39 per cent, of linseed oil and from 19 to 25 per cent, of
nitrogenous substances, chiefly proteins in the form of large
aleuron-grains ; these reserve foods are stored both in the
endosperm and in the cotyledons of the embryo.
The oil is used in the preparation of varnishes, oil-paint, and
printers' ink, for the manufacture of soft-soap and oilcloth, and
partially as food in some countries.
The nitrogen-free extract, consisting of the mucilage of the
epidermis of the seed and hemicelluloses of the cell-walls of the
embryo and endosperm, averages 22 per cent., the amount of
water generally 1 2 per cent., the woody fibre 5 or 6, and the ash
about 4*3 per cent, of the seed.
The residue of the seed, after extracting the oil, is made into
linseed 'oilcake,' the composition of which varies very much
according to the method adopted for extraction.
Linseed cake of fair average composition usually contains from
ii to 12 per cent, of water, 10 to 12 per cent, of oil, 28 or 29
per cent, of nitrogenous substances, 29 to 30 of carbohydrates,
9*5 to ii of fibre, and 77 to 8 '8 per cent, of asft.
CHAPTER XXX.
ROSACES.
i. General characters of the Order. Flowers regular, and
usually perigynous. Calyx gamosepalous, five sepals ; in some
genera an epicalyx is present. (See strawberry below.) Corolla
polypetalous, five petals. Andrcecium, usually of many stamens.
Gynaecium, apocarpous, sometimes more or less syncarpous, one
or many carpels. Fruit various. Seeds exendospermous or with
scanty endosperm.
The Order Rosaceae comprises about 1000 species of herbs,
shrubs, and trees. The leaves are generally compound, and
possess stipules.
There is no plant of the Order of much importance to the
farmer as a fodder crop, but all our most valuable edible fruits
of the orchard and garden belong to it. The genera, the struc-
ture of whose fruits it is important to notice, are mentioned
below.
2. Genus Prunus. Plums and Cherries. The plants of this
genus are shrubs or trees with simple leaves. The flowers are
perigynous ; the receptacle has the form of a hollow cup, around
the edge of which are arranged five sepals, five petals, and fifteen
to twenty stamens (Fig. 124.). The single carpel, which pos-
sesses a long terminal style and two ovules, is placed at the
bottom of the hollow receptacle. After fertilisation the latter
divides by a circular cut near its base at /, Fig. 124, and soon
withers and falls off, carrying the calyx, corolla, and androecium
with it Sometimes the withered receptacle and its appendages
remain for a time surrounding the growing carpel.
403
404
ROSACES
Eventually the single carpel which is left develops into a
drupe (the fruit) (J3, Fig. 1 24). The ovary wall (/) increases in
thickness, and when ripe exhibits three layers of tissue of different
texture, viz. : (i) an inner, hard, bony layer (e) next the seed
termed the * stone ' of the fruit or endocarp^ consisting of scleren-
chymatous cells ; (2) a soft parenchymatous layer (m) the
* flesh ' or mesocarp with sweet cell-sap ; and (3) an outer
thin skin or epicarp.
During the early growth, increase in size of the fruit proceeds
FIG. 124. A t Vertical section of the flower of a plum, x Receptacle; o petal ; a
stamens ; 6 ovary, inside which is seen an ovule. The part of the receptacle above the
lineyCr falls off after fertilisation. .
B % Fruit (drupe) developed from the gynaecium of the flower A. p The pericarp, of which
e is the endocarp or * stone ' ; m the mesocarp or ' flesh ' ; s seed ; J/ point where style
has fallen off; x small remaining part of the receptacle.
rapidly up to what is known as the ' stoning period ' when the
endocarp is beginning to harden, at which time growth in
diameter almost ceases. As soon as the ' stone' has become
firm the fruit begins again to increase in diameter, the chief
growth in thickness taking place in the mesocarp.
3. A glucoside, known as amygdalin, is present in the bark,
leaves, and seeds of many species of this genus : it is a non-
poisonous compound, but under the influence of the enzyme,
cmulsin, which is often associated with it, and in the presence
APRICOT 405
of water, amygdalin decomposes into benzaldehyde (oil of bitter
almonds), sugar, and the veiy poisonous prussic acid.
4. The chief species of Prunus are the sloe, bullace, plum,
cherry, apricot, almond, and peach.
They may be divided into two groups according to the way in
which the leaves are packed in the bud.
SECTION I. Leaves rolled in the bud.
Sloe or Black-thorn (Prunus spinosa L.). A small shrub,
with almost black bark, many spiny branches, and white
protogynous flowers which appear in spring before the narrow
lanceolate foliage leaves. The fruit is a small round drupe,
about \ an inch in diameter, with a glaucous * bloom ' and
smooth peduncle.
Bullace (Prunus insititia L.). A shrubby tree with a few
spiny branches and dark-brown bark. The young twigs are
usually covered with a soft down, and the broader almost ovate
leaves are also downy on the under surfaces. The flowers are
white and usually appear with the leaves. The round fruits are
black or yellow, about J to i inch in diameter, with downy
peduncles and glaucous bloom.
The damson is a form of bullace with oval fruits.
Wild Plum (Prunus domestica L.). This is a small tree
similar to the Bullace in the shape of its leaves and the colour of
the bark. The branches do not possess spines and are devoid
of downy hair. The fruits are oval or oblong, about i to ij
inches long, black, with smooth peduncles.
The wild plum is not a native of this country, although well-
established in woods and hedges as an escape from cultivation.
The cultivated plums have arisen from the above and several
other species most probably by cross fertilisation : the origin of
many varieties is however unknown.
Apricot (Prunus Armeniaca L.). An introduced tree origin-
ally derived from Mongolia and Turkestan (not Armenia as its
name implies). The branches are smooth and the flowers appear
28
406 ROSACES
before the leaves. The fruit is yellow, round or oval, and has a
hairy velvety surface.
SECTION II. Leaves folded (conduplicate) in the bud.
Wild Cherry : Dwarf Cherry (Prunus Cerasus L.). A small
shrubby tree, from 4 to 8 feet high, with slender branches. The
leaves are dark green, smooth on both sides, and possess short
petioles.
The inner scales of the flower-buds are leafy and the sepals of
the flowers are serrated. The fruit is round and red, with soft,
juicy, acid ' flesh.'
This species appears to be the parent of the Morello, Duke,
and Kentish cherries.
Oean: 'Wild Cherry* (Prunus Avium L.). A taller tree
than the last, often 20 to 30 feet high, with erect, short, rigid
branches. The leaves are pale green, somewhat hairy beneath,
and with a long petiole ; they hang down more than those of the
dwarf cherry. None of the scales of the flower-buds are leafy,
and the sepals of the flowers are entire. The fruit is heart-
shaped, black or red, and has firm bitter flesh.
This species appears to be the parent from which the Heart
and Bigarreau cherries have been derived.
Bird Cherry (Prunus Padus L.). A tree from 10 to 20 feet
high. It differs from the previously-mentioned cherries in having
its flowers in loose pendulous racemes from 3 to 6 inches long.
The fruits are round or ovoid and small, about \ of an inch in
diameter, with a bitter taste.
The Almond (Prunus Amygdalus Hook. **Amygdalus corn-
munis L.) has a hairy fruit with a leathery tough mesocarp:
when ripe the latter separates irregularly from the woody
wrinkled 'stone* which contains the seed. Two races are
known, namely, one with bitter the other with ' sweet ' seeds.
The Peach (Prunus Persica Benth. et Hook. - Amygdalus
Persica L.) very closely resembles the almond in all characters
except those of the fruit. The latter is usually covered with
STRAWBERRIES 407
velvety hair, and has a soft juicy mesocarp ; the nectarine, how-
ever, which is only a sport from the peach, has smooth-skinned
fruits.
Ex. 204. Examine the flowers of the plum, cherry, and sloe, cut longi-
tudinal sections of the flowers, and note the form of the receptacle and the
form and position of the various parts of the flowers, paying special attention
to the gynaecium.
Ex. 205. Watch the development of the ovary of a plum flower, when tb
latter begins to fade. What becomes of the receptacle ?
Ex. 206. Examine a half-grown plum or cherry. Observe the place where
the style was placed on the ovary, and also the position of the ventral
suture.
Cut sections both longitudinal and transverse of the ovary every week from
the time the flower fades up to the time the fruit is ripe. Note especially the
growth in thickness of the parts of pericarp, viz., the endocarp or 'stone,'
and the mesocarp or * flesh. 1
Ex. 207. Measure the diameter of three or four fruits every week and
determine when the increase in the diameter is greatest.
Ex. 208. Make a collection of stones of the different varieties of plums and
cherries. In what ways do they differ from each other ? Compare the stones
of the peach, apricot, and nectarine.
5. Genus Fragaria. Strawberries. This genus comprises
three or four species of plants all with edible ' spurious fruits/
of which the wild strawberry or any of the garden varieties may
be taken as an example.
The calyx of the flower is gamosepalous of five sepals. Out-
side the calyx, and alternating with it, is a whorl of five sepal-
like members, constituting what is known as an cpicalyx. Each
sepal-like member of the epicalyx represents two united stipules
belonging to the adjacent true sepals.
A vertical section of the strawberry flower is given in Fig. 1 25.
The receptacle is of peculiar form : it is a solid roundish or
cone-shaped structure, round the base of which extends a flat
rim. To the flattened rim is attached the corolla (&) of five
petals, and the andrcecium of many stamens (s) ; the numerous
small carpels constituting the gynaecium are inserted upon the
408
ROSACES
central raised part of the receptacle. Each carpel has a lateral
style, and contains a single ovule. As the calyx, corolla, and
androecium are inserted on the receptacle surrounding and free
from the centrally placed gynsecium the flower is perigynous.
The flowers are protogynous, and cross-pollination is usually
effected by insects. In some cultivated varieties the flowers
possess no stamens ; neither the fruits proper, nor the receptacles
of such pistillate flowers develop unless pollen is brought from
another flower, hence the necessity of planting kinds bearing
staminate or bisexual flowers near them in order to secure a
crop of ' fruit ' of such varieties.
After fertilisation the gynaecium develops into the fruit, which
is composed of small one-seeded achenes, and the receptacle
B
FIG. 123. A , Vertical section of a strawberry flower, a Sepal ; b petal; s stamens ;
c carpel.
B) Section of the
parts of
Section of the 'spurious fruit' developed from the flower A : the corresponding
of the flower and ' fruit ' are connected by lines.
grows to a large size, becoming at the same time succulent. The
succulent growth of the receptacle appears to depend on the
fertilisation of the ovules within the carpels ; should any of the
carpels be injured and fertilisation be prevented, the part of the
receptacle on which such carpels are situated does not develop,
and the result is a deformed strawberry. The achenes, which
RASPBERRY BLACKBERRY 409
at first are crowded together, become much separated from each
other by the growth of the receptacle,
It is the receptacle or terminal part of the flower-stalk which
is the edible part of a strawberry, the true fruit (ripened
gynaecium) being the achenes.
6. The common Cinquefoils (Potentilla reptans L., and P.
Tormtntilla Scop.) and Silver Weed (Potentilla anserina L,)
are weeds belonging to the Rosaceae, with yellow flowers resem-
bling the strawberry in structure ; their receptacles, however,
do not become fleshy, and the fruit is a collection of closely
arranged achenes.
To an unobservant eye the flowers of some of the Potentillas
resemble those of the buttercup species of Ranunculus : they are,
however, readily distinguished from the latter by the possession
of an epicalyx and a comparatively large receptacle.
7. Belonging to the Rosaceae is the genus Rubus , of which
the Raspberry (Rubus Idaus L.) and Blackberry (Rubus fruti-
cosus L.) may be taken as types for study of the flowers and
fruit. The flowers of these plants generally resemble those of the
strawberry in structure : no epicalyx is present however, and each
carpel possesses two ovules instead of one. The flattened border
of the receptacle on which the petals and stamens are inserted is
broader in the raspberry and blackberry than in the strawberry,
but the central lump on which the carpels are placed is very
similar in all these flowers.
After fertilisation the central portion of the receptacle, unlike
the strawberry, remains comparatively small, and does not become
succulent ; the carpels, however, develop into small succulent
drupes, which are red or yellow in the raspberry and black or
deep purple in the blackberry.
Thus the part which is eaten in the raspberry is a true fruit,
consisting of several one-seeded little drupes or drupels.
410 ROSACES
Ex. 209. Examine the flower of a strawberry. Make sections to illustrate
the shape and extent of the receptacle.
Ex. 210. Watch the growth of a strawberry from day to day until the fruit
is nearly ripe. Observe what becomes of the calyx, petals, and stamens.
Examine the form and content of the carpels and the achenes which de-
velop from them.
Make a vertical section of the nearly ripe 'fruit.' Note the distribution
of the vascular bundles in it.
Ex. 211. Compare a raspberry or blackberry flower with that of a straw-
berry. Watch the growth of the fruit after the flower fades, noting the
development of the little drupes from the carpels.
Examine the structure of a young carpel and compare it with that of a
drupel.
8. The genus Rosa includes the wild Dog-Rose (Rosa canina
L.) and several other indigenous species, as well as the many
introduced species and their hybrids and crosses much cultivated
as ornamental plants in the garden.
The flowers are markedly perigynous.
In the wild roses the calyx consists of five sepals ; the corolla
is polypetalous of five large petals, and the andrcecium possesses
numerous stamens. The receptacle is deeply-hollowed out like
that of the plum, but the upper part is constricted. The
gynaecium is apocarpous, and consists of many free carpels
inserted on the bottom and sides of the hollow urn-shaped
receptacle: the styles and stigmas of the carpels protrude
through the narrow opening of the receptacle. After fertilisa-
tion the carpels develop into achenes with hard, bony pericarps,
and the receptacle which surrounds them becomes somewhat
fleshy and red.
The 'hip* of the rose is therefore a spurious fruit, which
consists of a scarlet or red receptacle inclosing the true fruit
(the achenes).
Ex. 212. Cut a vertical section of the wild rose. Note the form of the
receptacle, and compare it with that of a plum, cherry, or sloe.
Observe the number, shape, and structure of the carpels ; also the position
of the sepals, petals, and stamens of the flower.
WHITE BEAM
411
What parts of the flower are still present in a ripe 'hip/
Ex. 213. Examine the structure of a double garden rose and compare it
with that of a wild one.
9. Genus Pyrus. To this genus belong the Pear (Pyrus
communis L.), Apple (Pyrus Mains L.), Medlar (Pyrus ger-
manica Hook.), and several other species, such as Mountain Ash
(Pyrus Aucuparia Gaert.), Wild Service (Pyrus torminalis
Ehrh.), and White Beam (Pyrus Aria Sm.).
FIG. 126. A, Vertical and transverse section of a
pear flower, n Sepal; a 'calyx-tube* of the recep-
tacle ; r lower part of the receptacle ; c carpels im-
bedded in r ; o ovules ; b petal ; s stamen ; st style.
B) Pome developed from the flower A .
The flower and fruit of the pear, illustrated in Fig. 126, may
be taken as an example of the genus.
The receptacle of the flower is hollowed out, and the gynaecium,
consisting of five carpels, is sunk in the hollow space.
In the plum (cf. Fig. 124) and rose, which also have similarly
hollowed receptacles, the carpels are free from the sides of the
41* ROSACES
latter ; but in the pear the ovaries of the carpels are fused with
the receptacle, and also united with each other except near their
ventral sutures (see the middle of the transverse section, Fig.
126, A) and along the styles, which are free. The ovary is
inferior and five-chambered : in each carpel are two ovules.
The upper part (a) of the receptacle is sometimes termed the
calyx-tube of the flower ; to it is attached the calyx of five sepals,
the corolla of five white petals, and the andrcecium of many
stamens.
After fertilisation the petals fall off, the stamens and styles
wither, and the rest of the flower develops into a peculiar
* false fruit ' termed a pome.
At the upper part of the pome is seen the * eye ' of the ' fruit,'
consisting of the so-called calyx-tube with the remains of the
sepals (n) and stamens (s) attached to it : the withered styles
(st) are also frequently visible. The carpels of the gynaecium
which constitute the true fruit are fleshy, but their inner walls
develop into a thin, tough, horny endocarp surrounding
the seeds. The main bulk of the pear for which the * fruit '
is grown is the very large receptacle which envelops the
gynaecium.
The flowers of the pear are protogynous and have white petals :
the pome is top-shaped. Self-fertilisation is possible even with-
out the visits of insects : cross-fertilisation is however most
common in the chief rosaceous genera. Cross-fertilisation is
necessary for the ' setting ' and development of the ' fruit ' of
several varieties of pears : after pollination from the same flower
or from plants of the same variety no fruits 'set/ hence the
importance of planting several distinct varieties in an orchard of
pears.
Most of the cultivated Pears appear to be hybrids and selected
crosses between several species of Pyrus.
10. The Apple differs from the pear in possessing flowers with
pink and white petals and styles which are united at their bases
QUINCE 413
within the calyx-tube : the pome moreover is somewhat spherical
or conical with an indented base where it joins the peduncle.
n. The Medlar (Pyrus germanica Hook.) is sometimes placed
in a separate genus and named Mespilus germanica L. Its
1 fruit ' is a roundish top-shaped pome to which are attached the
five large leaf-like sepals. The receptacle is hollowed out as in
the apple and pear, but it does not completely enclose the
carpels; the latter are consequently exposed within the broad
open calyx-tube. Each carpel, of which there are five, de-
velops a hard bony wall which protects the single seed within it
21. Allied to the medlar in structure of the fruit is the White-
thorn or Hawthorn (Cratagus Oxyacantha L.), so valuable for
hedges.
The ' fruit ' when ripe is a scarlet round or ovoid pome, but
the upper part of the receptacle or calyx-tube is more con-
tracted than in the medlar and the sepals are small. The carpels
are usually only one or two in number : they develop hard bony
walls.
13. The Quince (Cydonia vulgaris Pers.) belongs to another
genus of the Rosaceae.
The * fruit ' or pome is hard and possesses a woolly surface
when young but is smooth when ripe. It resembles the pear or
apple in shape and structure, but within each of its five carpels
are many seeds arranged in two rows. The sepals at the apex
of the fruit are leaf-like.
The testa of the quince seeds abounds in gum which with
water swells up into a mucilage.
Ex. 214. Compare the flowers of the apple and pear. In what do they
differ from each other ?
Ex. 215. Make longitudinal and transverse sections of the flowers of an
apple and a pear. Observe the position and extent of the receptacle and the
part of it termed the calyx-tube ; in each note also the number of carpels
and the ovules in the latter.
Bx. 216. Examine a half-grown apple and pear : observe the calyx-
tube. What part of the apple and pear flower is still visible in the fruit
414 ROSACE^E
Cut longitudinal and transverse sections of an apple and a pear Note
the number and position of the seeds in each loculus within the * fruits.'
Ex. 217. Examine the structure of a hawthorn flower.
Watch the growth of the * haws ' after the flower fades : cut sections and
examine the structure of young and old ' haws.' Compare a * haw ' with
an apple.
Ex. 218. Repeat Ex. 217, using a quince and medlar instead of the haw-
thorn.
14. Common weeds belonging to the Rosaceae and possessing
flowers and fruits somewhat different from any previously dis-
cussed are :
Meadow Sweet (Sptraa Ulmaria L.) ; Wood Avens (Geum
urbanum L.) ; Agrimony (Agrimonia Eupatoria L.), and species
of Burnet (Poterium).
The fruit of meadow sweet consists of five or six follicles each
containing usually two seeds ; that of wood avens is composed
of achenes which when ripe have long hooked styles. In agrimony
the fruit consists of one or two achenes imbedded in a small
spinous woody receptacle.
Lesser Burnet (Poterium Sanguisorba L.). A perennial
herbaceous plant common on dry calcareous soils in various
parts of the country. It grows to a height of 18 inches or 2 feet,
and has a slightly angular stem bearing pinnate leaves, with
from five to ten pairs of coarsely serrate leaflets. The flowers
are small of reddish-green colour and arranged in dense heads at
the end of long furrowed stalks. The upper flowers of the
head are female with one or two carpels : the lower ones male or
bisexual with twenty or thirty stamens. None of the flowers
possess a corolla.
The fruit consists of one or two achenes enclosed in a four-
winged receptacle. The margins of the wings are entire, the part
between the wings being netted or irregularly veined.
Forage Burnet (Poterium polygamum W. and K. = P. muri-
catum Spach.) is a continental species similar to P. Sanguisorba
but larger in all its parts, including the inflorescence and fruit.
FORAGE BURNET 415
The four wings of the fruit are usually toothed along the
margins and the parts between the wings deeply corrugated and
pitted (C, Fig. 206).
The truits constitute a common impurity of unmilled sainfoin
' seed/ especially that of foreign origin, and samples of the latter
should always be examined for them.
The Burnet recommended by seedsmen for forage is usually
this species, but the native species is also used occasionally.
Both these plants have been praised for growth on dry calcareous
soils, alone or in mixture with grasses and clovers, especially for
sheep food.
By themselves they are of little value as they are liable to
become hard and woody, and are rejected by all kinds of stock
unless the latter are pressed by hunger. In mixtures even, we
think, they have little or nothing to recommend them except for
use upon very dry chalky ground where nothing better can be
grown.
Ex. 219. The student should examine and become practically acquainted
with Meadow Sweet, Wood Avens, Agrimony, Lesser Burnet, Forage
Burnet and the common species of Potentilla.
CHAPTER XXXI
LEGUMINOS^.
i. THE Order Leguminosae ranks next to the Composite in
number of species, about seven thousand being recorded. The
Order is divided into three Sub-orders, namely, Casalpinea^
Mimosect) and Papilionacect The two former are almost entirely
tropical and possess little of interest or importance for the
farmer : the Papilionacese, however, includes some of the most
important fodder crops known, and the seeds of several species
are utilised as human food.
SUB-ORDER PAPILIONACEJB.
2. General characters of the Sub-Order. Flowers irregular,
protandrous, medianly zygomorphic, slightly perigynous ; calyx
gamosepalous, five-partite ; corolla, usually polypetalous, though
in red clover and some other plants of this order the bases of
the petals are united with each other and with the filaments of
the stamens ; the lower part of the corolla in such cases is
tubular. The petals are irregular and five in number, the
posterior one is large and conspicuous and is termed the
* standard ' or vexillum of the corolla ; besides this are two
lateral petals known as the ' wings ' or ala, and two anterior
petals more or less coherent by their margins and forming a
boat-shaped structure called the 'keel' or carina in which the
gynaecium and stamens are enclosed and protected. This form
of corolla, from its fanciful resemblance to a butterfly, is termed
papilionaceous, and is characteristic of the sub-order. The andro*
416
GENERAL CHARACTERS OF SUB-ORDER 417
cium consists of ten slightly perigynous stamens, either all the
filaments are united (monadelphous\ or nine are united and the
posterior or upper one free (diadelphous). The gynaecium is
superior, of one carpel, and contains one or many ovules. Fruit
generally a legume; seeds with a firm leathery testa, exendo-
spermous ; the embryo possesses thick fleshy cotyledons.
The cotyledons of the bean, vetch, and pea remain permanently
below ground, while others, such as those of the clover, sainfoin,
and lucerne, come above the ground soon after germination
commences.
The flowers of the Papilionaceae are all specially adapted
for insect pollination. The * standard ' acts as a conspicuous
attractive banner. The 'wings' and 'keel' petals are often
interlocked near their bases in such a manner that when an
insect of sufficient weight alights on the 'wings' these are
pressed downwards and in turn depress the 'keel' petals;
the stamens, style, and stigma are by this movement forced out
at the apex of the ' keel,' and the pollen is brought into contact
with the underneath part of the insect's body. The insect
visiting another flower brings the pollen on its body into contact
with the stigma which, on account of its length and position, is
generally forced out first from the apex of the 'keel'; cross-
pollination is thus effected.
Some plants, such as field and garden peas, sweet pea, common
and hairy vetch, dwarf kidney-bean, hop-clover, and hop-trefoil,
while undoubtedly posessing flowers specially adapted for insect-
pollination are capable of self-pollination, and are also fertile and
able to produce seeds when insects are excluded. Others, such as
red, white and crimson clovers, scarlet-runner bean, and broad
bean are more or less sterile when insects are prevented from
visiting the flowers.
All parts of the plants, and especially the seeds, contain
considerable quantities of nitrogenous substances, upon which
much of their feeding-value depends.
41 8 LEGUMINOS^E
Through symbiosis with a bacterium which penetrates the
roots, the Leguminosae are able to thrive upon ground which
is devoid of combined nitrogen : the nitrogen which they require
for growth is obtained indirectly from the free nitrogen of the air
(see p. 806).
Usually a cereal and especially wheat is taken after the growth
of a leguminous crop.
Some species, such as vetches and lupins, are occasionally
grown on poor, dry ground to be subsequently ploughed in as a
' green manure ' ; this practice largely increases the nitrogen-
content of the soil and at the same time augments the stock
of humus in the latter.
3. The genera most important from a farmer's point of view
are the following :
Pisum (peas), Vicia (vetches and common bean), Trijolium
(the true clovers), Medicago (the medicks lucerne and yellow
trefoil), Onobrychis (sainfoin), Anthyllis (kidney-vetch), and Lotus
(birds'-foot trefoil).
Some common plants of less importance belonging to other
genera are Gorse or Whin (genus Ulex), Bokhara clover (genus
Mdilotus\ Everlasting pea (genus Lathyrus\ Lupins (genus
Lupinus) ; and in gardens Scarlet Runner and Dwarf Kidney
Beans of the genus Phascolus*
4. Peas (genus Pisum). The cultivated varieties of peas are
usually supposed to belong to two species, namely : (i) the
Field Pea (Pisum arvense L.), which is said to be found in a
wild state in the south of Europe, and (2) the Garden Pea
(Pisum sativum L.), which is not known wild, and may possibly
be a modified form of the former species.
The Garden Peas, of which there are endless varieties, have
white flowers, and seeds of uniform yellowish white or bluish
green colour: they are also more delicate and suffer more
readily from frost and drought than the field pea.
Some of the garden forms for human consumption are grown
FIELD PEA 419
on farms near large towns, and are a profitable crop on suitable
lands under such circumstances.
The Field Pea, of which there are comparatively few varieties,
is more hardy than the garden pea, and the flowers have purple
or lavender coloured * standards ' and ' wings * of deeper purplish
red ; the colour of the seeds is greyish brown, dun-colou/ed, or
grey speckled with fine spots.
SEED AND GERMINATION. The seeds do not germinate freely
below a temperature of '5 C.
The young seedling resembles that of the bean in general
structure. It possesses a strong tap root, two cotyledons which
remain permanently below ground, enclosed by the testa of the
seed, and an epicotyl, which comes above ground in a curved
form.
ROOT, STEM AND LEAVES. The pea possesses a marked
tap root and a number of branching secondary roots. The
stems are round and too weak to stand erect without a
support.
The leaves are pinnately compound with large leaf-like stipules,
the leaflets, of which there are generally two or three pairs, are
ovate, with mucronate tips. The end of the leaf possesses one
or more opposite pairs of tendrils and a terminal one, all of
which are modified leaflets (Fig. 33). The tendrils are sensitive
to contact, and wind round any small support which they touch ;
by their aid the plant is enabled to support itself in a more or
less erect position by clinging to neighbouring objects
INFLORESCENCE, FLOWERS AND FRUIT. The inflorescences
are axillary racemes with few flowers, often only one or two.
Each flower is perigynous; the calyx gamosepalous and five-
lobed ; the corolla papilionaceous (Fig. 127); the andrcecium is
diadelphous consisting of ten stamens, one of which is free, the
rest united by their filaments.
The gynaecium of the flower is superior and consists of a single
carpel with many ovules ; the stigma is placed at the end of the
42O
LEGUMINOS^E
curved style which bears a number of hairs on its concave or
upper side. The fruit is a typical legume (Fig. 37).
VARIETIES. The following are the commoner varieties of
field peas :
Common Grey Field Pea. A prolific late variety suited to
light chalky soils. The c straw ' is liable to be long and on good
soils becomes * laid ' before the pods and seeds are ripe.
5
o
FIG. 127. i. Flower of a field pea. 2. Section of same ; s ' standard ' ; w ' wing,*
united filaments of nine
style of gynaecium. 4. The
and k 'keel' petals respectively. 3. Andrcecium; / united filaments of nine
stamens ; f filament of single free stamen ;
gynaecium ; o ovary, s style with hairy stigma.
The legumes are almost cylindrical, and contain from six to
eight dun-grey or bluish-green self-coloured seeds.
This kind is sometimes grown in mixture with Scotch horse
beans, which act as supports for the peas.
Early Grey Warwick. This is a rapid grower, and adapted
to late districts where the soil is in rich condition. It has dun-
coloured seeds spotted with purple.
GREY ROUNCIVAL OR DUTCH PEA 421
Partridge. An early prolific variety of good quality, and suit-
able for growing in late districts.
The stems are soft, and usually about 4 feet long with broad
leaflets. The pods often grow in pairs, each containing from
five to seven roundish seeds of a pale brown colour beautifully
speckled with small darker spots and lines.
Grey Maple. This variety has speckled seeds like those of
the Partridge variety, but larger ; it is adapted to the better kinds
of soil in districts with mild climate.
Grey Rouncival or Dutch Pea. A very late field pea with
very long ' straw ' and large dun-coloured wrinkled seeds. The
stems are often 7 or 8 feet long, and the pods generally grow in
pairs and contain five or six seeds. This variety is only suited
to light soils in early districts.
SOIL. Peas give the most satisfactory yield of seeds upon
soils of a medium or somewhat inferior character. In all cases
it is necessary that the ground should contain a considerable pro-
portion of lime. Upon good rich soils or those of a peaty and
damp character the stems and leaves grow too long and become
laid : the crop then yields few peas.
In cases where the ground is comparatively rich, but not stiff
enough to yield a good crop of beans, a mixture of beans and
peas at the rate of i J bushels of the latter to 2^ of the former
often gives good results. The stiff erect bean stems act as sup-
ports for the luxuriant weak stems of the peas, and the latter are
enabled to secure an adequate amount of light and air for seed
production.
SOWING. The seed is best sown in February or March in drills
at a distance of 14 or 18 inches apart and 2 to 3 inches deep : the
amount needed is 2 to 4 bushels per acre according to the size of
the individual seeds. On very clean ground the seed is occasion-
ally sown broadcast at the rate of 4 or 5 bushels per acre.
YIELD. Peas are one of the most uncertain of farm crops, only
one crop out of every three or four being satisfactory. The yield
on the best soils adapted to the crop averages about 30 or 35
bushels of seed and about a ton of straw per acre, but on unsuitable
soils in bad seasons the yield of seed may be practically nothing.
COMPOSITION. Peas are slightly less nitrogenous than beans,
but they contain more soluble carbohydrates and less ' fibre '
than the latter.
29
422 LEGUMINOS^E
Peas contain on an average 14 per cent, of water, 20 per cent,
of albuminoids, about 54 per cent, of soluble carbohydrates, and
5i per cent, of ' fibre.'
Vetches (Genus Vicia.)
5. Bean (Vicia Faba L., or Fab a vulgaris Moench). A well-
known annual plant whose seeds are excellent food for all kinds
of stock on the farm. The stems and leaves (' haulm or straw ')
when well-harvested make fodder little inferior to good hay.
SEED AND GERMINATION. The nature of the seed and seed-
ling of a bean has been discussed in Chapter II.
ROOT, STEM AND LEAF. The primary root is strongly de-
veloped. The stems, which stand erect, are unbranched, and
from 2 J to 5 feet high, according to the variety. They are ' fleshy '
and stiff, four-sided and slightly winged.
Usually three stems spring from one seed, viz., the main stem,
and two lateral ones.
The leaves are pinnately compound, with one, two or three
pairs of elliptical entire leaflets.
INFLORESCENCE, FLOWER AND FRUITS. The inflorescences
are axillary racemes of two to six flowers. The flowers are of
the common papilionaceous type; the petals are usually all
white, with the exception of the wings, which have a large black
spot upon them.
The fruit is a legume which, when young, is fleshy and has a
thick velvety lining. After ripening the valves of the legume
become tough and hard.
VARIETIES. Several varieties of the bean, such as the Long
pods and Broad Windsor, are cultivated mainly in gardens and
cannot be noticed here. The following kinds are those most
generally grown as farm crops :
Scotch Horse Bean. A very hardy, fairly prolific variety, with
stems about 4 feet high. The pods contain on an average three
seeds. Each seed is buff or pale brown in colour, and about
MAZAGAN 423
half an inch long, slightly flattened on the sides with a black
hilum.
The Scotch horse bean grows best on strong, well-drained
clays.
Tick Bean or English Horse Bean. This variety, of which
there are a large number of named strains, is closely related
to the above.
Its seeds are not flattened on the sides but are almost
cylindrical, rounded at the ends and slightly smaller than the
Scotch horse bean.
The tick bean is very prolific and more suited to the climate
of the south of England, where it grows upon lighter soils than
those essential for a good crop of the Scotch horse bean.
Winter Bean. A variety resembling the tick bean, which, on
account of its hardy nature, can be sown in October to stand
the winter. It is usually harvested in the following July or
August.
Mazagan. This is an early variety of fine quality, sometimes
grown in gardens. When grown as a farm crop it requires moder-
ately stiff land in good condition to obtain the best results.
The stems of the plant are slender, and 4 or 5 feet high. The
pods are long and narrow, and generally contain four seeds, each
of which is about three-quarters of an inch long, with flattened
and slightly wrinkled sides.
SOIL. The soils best suited to the growth of beans are well
drained, clayey loams. On light soils the total produce is small,
while on those rich in humus the plants grow tall and leafy, but
yield few seeds.
SOWING. With the exception of the winter variety beans are
sown in February or March. The crop is cut in late autumn,
when the stems are brown with a few small green patches upon
them ; the hilum should be black, and the seeds free from the
funicles in the pod before cutting the crop.
The seed is sown in drills usually about 18 inches or a feet
424 LEGUMINOS^E
apart ; the amount used is from 2 to 4 bushels, according to the
size of the bean.
YIELD. The average yield is about 30 bushels of seed and
from 20 to 30 cwt. of ' straw.'
COMPOSITION. Bean seeds contain 14 per cent, of water and
about 23 per cent, of albuminoids, mainly in the form of fine
aleuron-grains in the cells of the cotyledons of the embryo. The
carbohydrates, the chief of which is starch, average 48 per cent;
the fat, i per cent. ; and the fibre, 7 per cent.
6. Common Vetch or Tare (Vicia satjva L.). An annual
vetch with trailing or climbing stems and compound pinnate
leaves. The primary stems branch extensively from the axils
of the lower leaves, and the secondary and tertiary branches also
branch freely.
The first few leaves of the seedling plant have one or two
pairs of narrow leaflets and no tendrils ; those appearing later
are, however, furnished with two or three terminal tendrils and
six or seven pairs of leaflets, which are broader and oblong or
obovate in form, with a stiff mucronate point.
The stipules are small and pointed, with a dark purple blotch
in the centre.
The flowers, which are reddish purple, are borne singly or in
pairs on very short stalks in the axils of the leaves.
The fruit is a more or less hairy legume, containing from four
to ten smooth round seeds.
The cultivated vetch (V. sativa L.) is probably merely a
form of Vicia angustifolia Roth., which lis a common wild plant
in dry soils throughout the country.
There are two races of the cultivated vetch or tare, namely,
Winter Vetches and Spring Vetches. '
The Winter Vetch is a hardy form, capable of enduring
frost ; it has smoother, more cylindrical pods, with smaller
seeds than the summer variety, and gives less bulk of stem and
leaves.
SPRING VARIETY 425
This form is usually sown in September, October, or Novem-
ber, either alone or mixed with rye, winter barley, or oats for
early spring fodder.
The cereal is not only nutritious but acts as a support for the
vetches, and keeps the latter from trailing on the ground and
rotting at the base of the stem.
The Spring Variety grows more rapidly and luxuriantly
than the winter one, and is a more delicate plant. When used
for green fodder it is sown either alone at the rate of 4 bushels
per acre, or in mixture with oats or barley at the rate of 2\
bushels of vetches to i\ bushels of the cereal.
Small areas are sown from February onwards at short intervals
so as to provide a succession of crops during the summer.
It must be borne in mind that the spring variety is uncertain
for autumn sowing, and that the true winter variety if sown re-
peatedly in spring produces seeds which give rise to somewhat
delicate plants.
As the botanical morphological features of its seeds present no
points of constant difference by which the winter form may be
distinguished from the spring one, the farmer is compelled to de
pend on the honesty of the vendor when purchasing either kind.
Vetches grown for hay should be cut when in bloom ; at this
stage of growth it is superior in nutritive value to good meadow
hay ; when grown for seed, the yield of which is always very
uncertain, vetches may be sown alone or in mixture with beans
whose stiff stems act as supports and enable the crop to obtain
a better supply of the light and air necessary for healthy
growth.
The seeds of the vetch have practically the same composition
as those of the field bean.
Ex. 220. Sow the seeds of bean, pea and vetch in garden soil or pots ; dig
up the seedling as soon as two full-grown leaves appear on the stems above
ground, and examine the root system and the form and size of the leaves on
the stem above the cotyledons.
426 LEGUMINOS^E
Ex. 221. Dig up completely a half-grown plant of bean, pea and vetch,
and study the manner of branching in each.
Ex. 222. Compare the flowers of the bean, pea and vetch, and note any
points of difference between them Compare their leaves also.
Ex. 223. Make a collection of seeds of the different varieties of field bean,
field pea, and vetch.
7. Vetchlings or Everlasting Peas (genus Lathyrus). This is
an extensive genus of climbing plants much resembling vetches,
but with fewer leaflets and a flattened style. Eight or nine
species are wild in this country, and are known as vetchlings or
everlasting peas, although some of them are annuals. They
are all eaten by cattle.
The commonest species is the meadow vetchling (Lathyrus
fratensis L.), which is frequent in meadows and hedges. It
grows 2 or 3 feet high, and has narrow lanceolate leaflets and
racemes of bright yellow flowers.
The Wood Vetchling (Lathyrus sylvestris L.) grows in
woods and thickets ; it has winged stems, and often climbs to
a height of 5 or 6 feet The leaves possess tendrils and have
one pair of large lanceolate leaflets from 3 to 6 inches long and
half an inch broad.
Usually four or five flowers are present on each long peduncle :
the 'standard' petal is rosy-pink, the 'wings' purple. This
plant has been selected and cultivated on the continent as a
perennial fodder crop,* and is termed Wagner's Everlasting Pea
(Z. sylvestris L., form Wagncrf). Like lucerne it withstands
drought, and when once established gives very large yields of
highly nutritious food.
The seed is at present expensive, and germinates very slowly
in the open field.
Wagner's everlasting pea possesses few, if any, advantages
over lucerne and other leguminous crops at present in use on the
farm, and we see little need of its introduction.
RED OR PURPLE CLOVER 427
Clovers (Genus Trifolium).
8. Red or Purple Clover ( Trifolium pratensc L.). Red clover
is the most extensively cultivated species of Trifolium^ and
ranks first among fodder plants for excellence of yield, nutritive
value, and adaptability to various soils and climates. It is
grown alone or in mixture with grasses for leys of short duration
Soils upon which a crop has been raised refuse to grow a
second crop of remunerative size until a certain period has
elapsed, usually not less than four years, often much more.
Such soils are said to be 'clover-sick/ and although there is
no doubt that the dying away of clover sown on ground ex-
hibiting this peculiarity is due to several different causes, none
of the latter are yet very clearly understood.
SEED AND GERMINATION. The seeds absorb about their own
weight of water, and germinate in two or three days. The
seedling possesses a well-developed primary root and hypocotylj
the two elliptical cotyledons come above ground. The first
foliage-leaf of all the clovers is different from the succeeding
ones in being simple and rounded instead of compound and
ternate as in those which arise later upon the plant
ROOT AND STEM. The primary root of red clover develops
into a strong tap root with three lines of secondary roots which
spread extensively through the soil. ' Nodules ' are abundant
upon the roots. When sown in spring with a cereal, the epicotyl
of the young plant develops very little, but a great many
buds and short branches arise in the axils of the closely-packed
leaves, and by the contraction of the root the short stem and
its buds and leaves are pulled down so that they lie close to
the ground in the form of a rosette during autumn and winter.
Usually in the following spring but sometimes in the autumn
of the year in which the seed is sown, the buds grow out into
ascending branches, each from i to 2 feet high, bearing leaves
and terminating in dense flower-heads.
428 LEGUMINOS^E
LEAF. The leaves are stipulate and compound, with three
ovate leaflets, each of which is bordered with hairs.
The stipules are membranous with greenish-purple veins and
united to the petiole except at their tips which end in a fine
point (i, Fig. 128).
INFLORESCENCE AND FLOWER. The inflorescences are
terminal, ovoid or spherical capitula about i or i| inches in
1. 2. 3.
FIG. 128. Stipules of the leaves ot (i) red clover; (2) alsike clover; (3) crimson clover
or ' Trifolium ' ( T. incamatum) (all natural size )
length and composed of many small flowers crowded together.
Beneath each inflorescence are two leaves.
The flower is protandrous and has a gamosepalous calyx with
five free teeth at its apex, the inferior one being longer than the
rest.
The corolla is medianly zygomorphic and consists of a
standard, wings, and keel; the petals, however, instead of being
free as in the pea, are united at their bases to form a tube
nearly half an inch long (i, Fig. 129).
The andrcecium is diadelphous; nine united stamens are
fused with the corolla tube and the posterior one is free.
RED CLOVER
429
The single carpel of the gynaecium has a long style and a one-
celled ovary containing two ovules.
The fruit of red clover, is a one-seeded capsule (Fig. 130)
the upper part of which separates from the lower along an
irregular transverse line (pyxidium).
VARIETIES. Eed Clover ( Trifolium pralense. L.) is a wild plant
common in meadows and pastures
throughout Europe. In a wild state
it is variable in its habit of growth
and durability, but usually lasts from
three to four years. The seeds of
this truly wild indigenous plant
would no doubt be very useful in
mixtures for leys and permanent
pastures, but none are met with in
commerce except in name.
The cultivation of the plant as a
fodder crop was introduced into
this country from the Continent in ?/. rcd r cl 9 ve /- '.?. l >' ie ; ^ s vgma. 3 .
' Ripe fruit (pyxidium) containing the
the early part of the seventeenth single seed 4. s . Gynaecium.of white
J r clover (two and a half times the
century, and from that 'time to the natural sue.;
present its cultivation has spread
extensively.
So far as our experience goes no
seeds appear to be in commerce
which have been derived from the
wild plant within recent times, all
those sold being the progeny of
plants which have been under the
influence of cultivation for long
periods of time.
Among these samples obtainable from the seedsman are a con-
siderable number of varieties varying in hardiness, yielding
capacity, and slight botanical features.
FIG. 1291. Firmer of red clover.
Calyx; j 'standard;' w ' wings ;
k ' keel ' of the corolla. 2. Gynaecium
FIG. 130. Fruit (pyxidium) of red
clover ; on the upperpart a portion of
the withered style is seen (enlarged.)
430 LEGUMINOS^
Although they are extremely variable in form and pubescence
of leaves, solidity of stem and shape of the capitula, the different
commercial forms may be divided into two classes or groups,
namely: (i) 'Ordinary Red* or 'Broad Red Clover/ and
(2) 'Perennial Red/ 'Single cut Cow-grass' or 'Mammoth'
Red Clover (' Trifolium pratcnsc pcrenne*}.
The former class embraces the rapid-growing forms of short
duration, being little more than biennial plants. They give two
cuts or more per annum, and are specially suited for short leys.
After being mown once they produce a second crop, from which
a good yield of seed may often be obtained.
The leaflets of the plants are oblong, bluntish and pubescent
on both surfaces, the flower-heads round and sessile, and the
stems frequently hollow.
Representative of the second class is Single-cut Cowgrass,
a more permanent and hardier plant, which produces her-
bage for several seasons, and therefore useful for long leys and
permanent pasture. The leaflets are longer, narrower and less
hairy than those of Broad Red Clover, the stems more or less
solid, and the flower-heads ovoid and often on short stalks. It
blooms ten to fourteen days later than Broad Red Clover, gives
only one cut of hay or fodder per annum, and produces com-
paratively few seeds.
The existence of numerous intermediate forms renders it
impossible to state with certainty to which class or group certain
individual plants should be assigned.
The forms to use for particular purposes is a matter of no small
importance to the farmer, but as it is impossible to distinguish
them accurately either in the seed or when growing, he must
depend upon the reputation of the vendor (see pp. 627 and
656) when he purchases the seed.
CLIMATE AND SOIL. Red clover grows readily upon almost
all soils except those which are very dry or which contain an
execs'? of stagnant water. It thrives best, however, on some-
what heavy loams containing a fair proportion of lime.
It is sensitive to spring frosts, and varieties obtained from the
warmer parts of Europe and America often die off completely
during autumn and winter in England.
SOWING. The seed is sown generally with a cereal crop in
spring ; the amount needed for a crop when used alone is 16 Ibs.
per acre, if the seed is pure and of good germinating capacity.
WHITE OR DUTCH CLOVER 431
9. Zig-Zag Clover: Marl-Grass: Meadow Olover (Trifolium
medium L.). A perennial clover which grows most commonly
upon dry banks and in dry elevated pastures. At first sight it
may be mistaken for red clover, the flower-heads being of similar
colour. The stem is, however, straggling and bent in a zig-zag
manner at every node. The leaflets are narrower and longer
than those of red clover, and the free part of the stipules is
longer, more pointed, and narrow.
The flowers are a deeper purple colour and not so densely
crowded together in the capituium; the latter, moreover, is
stalked, the first pair of opposite leaves being a short distance
below the base of the flower-head instead of close to it as in
red clover.
Seed of this species is not met with in commerce, and the
plant is of little agricultural value.
10. Alsike or Swedish Clover: Hybrid Olover (Trifolium
hybridum L.). A perennial clover introduced into England
from Sweden in 1834.
It is a distinct species and not a hybrid as its name seems to
imply.
The stems are smooth, of upright habit, from i to 3 feet
high.
The free part of the stipules of the leaves are drawn out to a
long tapering point (2, Fig. 128), and have pale green veins.
The flower-heads, which are round, arise on peduncles
springing from the axils of leaves on the main stems.
The flowers are pale pink or white, resembling those of white
clover; the fruit is an indehiscent pod, containing from one to
three small seeds.
Alsike, of which there are no specially cultivated varieties, is
a more permanent plant than red clover, often lasting five or six
years on suitable soils. It is also much more hardy and better
suited to stiff damp soils, where other species of clover would
scarcely thrive at all.
Pure sowings are rarely made, but it is of great value in
mixtures of grasses and clovers on all stiff moist soils, although
the yield is not so good as that of the red species.
11. White or Dutch Clover (Trifolium rtpcns L.), (Fig. 131).
A well-known perennial clover, common in all good pastures
throughout the country. It differs in habit of growth from red
clover and alsike. Like these species it has a well-formed tap
432
LEGUMINOS^E
root, but the stems, which are smooth, creep over the surface or
just beneath the soil, and from their nodes adventitious roots
are given off. The leaves have very long petioles and small
ovate membranous-pointed stipules.
The round flower-heads are produced at the ends of long
stalks, which arise in the
axils of the leaves and grow
upwards (Fig. 131).
The flowers are white or
pinkish ; when the corolla
fades it turns brown, and
the whole flower becomes
deflexed.
The fruit is an elongated
pod containing from four to
six small seeds.
Fig. 132 illustrates the
early stages of growth of
a seedling, which may be
taken as typical of all the
cultivated clovers.
Three varieties of white
clover are met with in com-
merce, namely (i) 'Wild
FIG. 131. Portion of white clover plant, showing White,' a small permanent
the^' creeping 'habit of the stem, r Adventitious form ^hoSG Seeds are
harvested from old natural
pastures stimulated by applications of basic slag; (2) 'Culti-
vated White Clover,' the larger commonly cultivated form ;
and (3) Giant, Mammoth or Ladino White, a still taller Italian
form adapted for heavy soils or irrigated land in a warm climate.
(See Erith's Monograph on White Clover.)
White clover is more permanent than either red clover
or alsike, and grows upon almost all soils. It is sometimes
grown alone for sheep food, but its chief use is in mixtures
for laying down pastures for grazing purposes.
12, Crimson or Italian Clover: Trifolium (Trifolium incar*
natum L.). An annual species, with erect hairy stems from i to 2
feet high. The stipules of the leaves are broad and the free
part is rounded, often with a dark purple margin (3, Fig. 128).
The flower-heads are terminal, and placed some distance above
CRIMSON OR ITALIAN CLOVER
433
the last leaf of the stem : they are oblong or cylindrical, with
rich crimson, rose or white flowers.
Early and late varieties are met with in commerce, one of the
latest being a white-flowered form with pale cream-coloured seeds.
FIG. 132. Seedling of White or Dutch Clover at different stages of growth. In 2 the
first foliage leaf is seen to be simple ; in 3 the ordinary trifoliate leaves have appeared.
A variety, Trifolium Molinerii Balb., with shorter stems
and pale, almost white, flowers, is native in Cornwall, and is
434 LEGUMINOS^E
probably the original form from which the cultivated crimson
clover has been derived.
Crimson clover is tender and cannot be grown except in the
warmer parts of this country. In the south of England it is
grown generally as a catch-crop, the seed being sown on the
stubbles in autumn, and the produce fed off or cut for hay in
the following May and June.
13. Yellow Suckling (Trifolium dubium Sibth. = T. minus
Sm.). An annual clover with ascending, or prostrate, wiry
stems, sometimes a foot or 18 inches long, and small yellow
flowers. The flower-heads are small, and formed of about a
dozen flowers closely crowded together.
Yellow suckling is a useful plant in pastures. The produce is
scanty but nutritious to farm animals, and the plant indirectly
adds nitrogen to the soil which benefits the grasses associated
w ith it.
Trifolium filijorme L. is another species very nearly resemb-
ling T. dubium Sibth., but with only five or six flowers in each
capitulum, and slender short stems not more than 5 or 6 inches
long. Both are met with on dry, gravelly pastures.
14. Another annual species, namely, Hop-Clover, sometimes
termed Hop- Trefoil (Trifolium procumbens L.), is met with
on dry, gravelly pastures. It resembles the above two species
in general appearance, but the flower-heads look like miniature
hops and possess about forty flowers of a tawny, yellow colour.
The three last species are often confused with black medick
(Medicago lupulina L.), which they resemble in habit as well
as in colour and size of flower-heads. Black medick can, how-
ever, be easily distinguished by its leaflets : these are obcordate
as in the clovers, but the midrib is prolonged into a sharp
(mucronate) point, while the yellow clover leaflets are without
this projection.
Bz. 234. Examine and compare the habit of growth in red, white, Alsike,
LUCERNE OR PURPLE MEDICK 435
and crimson clovers. Note which are upright growers and which are
creeping.
Make drawings of the stipules, and also note any differences of form and
colour of the leaflets in each species.
Ex. 225. Sow seeds of the above-mentioned clovers in garden soil or in
pots in spring, and observe the form of the cotyledons, the relative size of
the hypocotyl and root in the young seedlings. Watch the development of
young plants up to the time of flowering, noting particularly the production
of branches in each species.
Sz. 226. Compare the flowers, fruits, and seeds of the chief clovers. Note
the manner of dehiscence in the several pods, and the number of seeds in
each.
Medicks (Genus Medic ago ^
15. Black Medick : Nonsuch Glover: Hop-Trefoil, Yellow
Trefoil (Medicago lupulina L.). An annual or biennial plant
wild on waste ground all over the country, especially in cal-
careous districts.
The stems are much branched, from 6 inches to a feet long ;
the lower parts spread over the surface of the ground but do not
develop adventitious roots ; the upper parts are ascending.
The leaves are trifoliate and the leaflets have a projecting mid-
rib which distinguishes the plant from the somewhat similar
yellow suckling and hop-clover. The flowers are yellow in small
compact oval flower-heads.
The fruit is a kidney-shaped, indehiscent black pod about an
eighth of an inch across with a spirally curved tip ; it contains
a single seed.
Black Medick is sometimes sown alone on poor calcareous soils
and used for sheep and lamb food. In suitable districts where
the soil is dry and inferior, a small amount is a useful addition
to grass mixtures for short leys. Occasionally a small quantity
is sown with sainfoin to increase the bulk of produce during the
first year when the sainfoin is not fully established.
1 6. Lucerne, Alfalfa or Purple Medick (Medicago sativa L.).
-A perennial introduced plant with erect branched stems i to 3
436 LEGUMINOSiC
feet high. The primary root is strongly developed and forms
a tap root which in old plants is often three-quarters of an inch
in diameter : this and the secondary roots penetrate several feet
into the earth on ground with an open subsoil. The leaves are
trifoliate ; each leaflet is obovate, dentate, with a notched tip
and a projecting midrib (f y Fig. 133).
The flowers are usually purple, but sometimes yellow, in
dense axillary racemes, the peduncles of which are longer than
the leaves.
The fruit is a dehiscent legume coiled two or three times into
a loose spiral : it contains several seeds.
Lucerne is one of the most valuable fodder plants for warm
climates and succeeds well in the south of England on ground
with an open subsoil. It suffers very little from drought when
once established and gives two or three heavy cuts of fodder
every season, the first of which is ready more than a fortnight
earlier than red clover.
It is most frequently used green, but can be made into hay ;
in the latter case it must be cut before flowering or it becomes
hard and woody, and special care must be taken to prevent loss
of leaves in handling.
In the first season the young plants develop large root-
systems and few stems and leaves above ground, consequently a
small crop only is produced.
Instead of the part of the stem above the cotyledons remain-
ing short for some time and its leaves forming a rosette on the
surface of the ground as in red clover, the internodes of the
epicotyl in lucerne elongate at once (3, Fig. 133), and the main
stem grows erect with comparatively few branches in the first
season. The crop therefore in the earlier stages of growth often
looks thin and disappointing.
Vigorous branches, however, spring up later from the lower
nodes of the stem and from the axils of the cotyledons (4, Fig,
133), especially after being cut once.
LUCERNE OR PURPLE MEDICK
437
In the second and third years a stout rootstock is formed from
which a large number of stems are sent up and the plants yield
a heavy crop of nutritious fodder.
Under some circumstances a lucerne ley will last a very long
FIG. 133. Four successive stages of development of Lucerne Seedling (Mtdicago sativa
L.). The first foliage-leaf (</) is simple, the second and all others trifoliate, as at f*
a Hyppcotyl ; b root \ c cotyledons ; a first foliage-leaf; e plumule ; /second foliage-leaf;
g first internode of epicotyl. In 4 note the buds in the axils of the cotyledons.
time but it usually becomes overrun with weeds in six or seven
years, after which time it is ploughed up.
Seed is sown from April to the end of June at the rate of 30
Ibs. per acre in drills 6 or 8 inches apart to allow of the use of
horse and hand hoes. ~
438 LEGUMINOS-^E
For this and all perennial crops whose growth is slow at first,
the ground should be especially clean before sowing or weeds
may ruin the crop before it is established.
Melilots (Genus Melilotus).
17. The melilots have upright stems with trifoliate leaves, re-
sembling those of lucerne. The flowers are small, yellow or
white, arranged in one-sided axillary racemes.
The fruit is a round or oval legume, which is only partially
dehiscent ; it usually contains from one to four seeds.
White Melilot \ Sweet Clover (Melilotus alba Desr.), which is a
rather uncommon plant doubtfully native in Britain, is some-
times introduced under the name of Bokhara Clover, and recom-
mended as a forage crop. It is biennial, and produces a large
bulk of leaves and stems, which have a fragrant odour like that
of sweet vernal grass ; owing to its bitter taste it is, however,
disliked by cattle, and also has the objectionable feature of rapidly
becoming hard and woody.
The seed is cheap, and possibly the plant may be found of
service for ploughing-in as a green manure.
Hubam Clover is the name given to a selected annual form of
white melilot.
Another commoner species, namely, Yellow Melilot (Melilotus
ojficinalis Willd.), grows 2 or 3 feet high, and possesses deep
yellow flowers. It is an annual, and met with in corn fields.
Sainfoin (Genus Onobrychis).
18. Sainfoin (Onobrychis sativa Lam.). A perennial plant,
probably indigenous in the midlands and south of England on
dry chalky soils.
The primary root is thick and fleshy, and penetrates to a depth
even greater than lucerne roots in open dry subsoils.
The young plant forms a rosette of leaves close to the ground,
and resembles red clover in its early habit of growth.
From the rhizome several almost erect stems are sent up, each
of which is from i to 2 feet high, ribbed, and slightly downy.
GIANT SAINFOIN 439
The first foliage-leaves of the seedling are small and simple
with long petioles; the second and third are trifoliate, all the
subsequent ones being pinnately compound with six to twelve
pairs of opposite leaflets and a terminal one. The leaflets are
narrow, obovate, and entire.
The inflorescences are axillary, compact racemes, the peduncles
of which are long, slender, and erect. Each flower is about half
an inch long, rosy-red, with darker pink veins, papilionaceous,
the * wing ' petals very short
The fruit is almost semi-circular in outline and about a quarter
of an inch long, its pericarp covered with a coarse raised net-
work of lines on which are spiny projections (Fig. 206) ; it is
indehiscent, and contains a single olive brown seed, in shape
like a small bean.
Sainfoin' is a valuable fodder plant for growth on dry, barren
calcareous soils.
It resists frost better than lucerne, but damp sub-soils are
destructive of both plants.
It is extensively used as sheep food, and cut green for soiling
cattle and horses. The produce makes excellent hay of very
high nutritive value when cut just in flower.
Two cultivated varieties are met with, namely, (i) The Old
Common Sainfoin, and (2) Giant Sainfoin.
The former variety is more lasting than the latter, a ley of it
being generally useful during four to seven years. It gives only
one cut per annum, after which the subsequent growth is
grazed.
Its stems are shorter, and the flowering period a week or ten
days later than the giant variety.
The giant sainfoin is a more rapid and luxuriant grower, and
is usually kept down only one or two seasons, during which it
yields two or more heavy crops per annum. If seed is required
the plant is cut once and the second growth of the season
reserved.
440 LEGUMINOSJE
When seed of the Old Common variety is wanted the first
growth of the year must be reserved for the purpose.
The seed is drilled in March or April, usually on a cereal
crop at the rate of 4 bushels (100-110 Ibs.) of 'seed in the husk/
or 50 Ibs. of ' milled ' (true) seed per acre.
The seed should be drilled about i inch deep in rows 9 to 1 2
inches apart.
Ex. 227. Dig up and examine young seedling plants of Sainfoin, Lucerne, and
Black Medick. Note the form and extent of the roots and branches of the plants.
Examine full-grown plants of each species, paying special attention to the
structure and form of their flowers, fruits, and seeds.
Serradella (Genus Ornithopus\
19. To the genus Ornithopus belongs Serradella (Ornithopus
sativus Brot.), a wild Portuguese and Spanish species, intro-
duced to many parts of the Continent as a useful plant for
growth upon dry sandy ground, and sometimes mentioned in
this country. It is grown largely for ploughing-in as a 'green
manure,' and is also utilised green as fodder or made into hay.
Serradella is a slender annual, about 12 or 18 inches high,
with compound pinnate leaves and small pale rose-coloured
flowers, of which from two to five grow together in a cluster at
the end of long axillary peduncles.
The fruit is curved, and breaks up transversely into many one-
seeded ' joints ' j three or four fruits growing together resemble
a bird's foot. An allied species O. pcrpusiltus L. grows wild in
sandy and gravelly places in this country.
Kidney Vetch (Genus Anthyllis).
20. Kidney Vetch (Anthyllis Vulneraria L.). An herbaceous
perennial common in dry pastures and on banks in calcareous
districts.
It possesses a strong underground branched rhizome, from
which ascending stems arise from 8 to 18 inches in length.
The latter are more or less softly hairy and bear few leaves.
During the first year the young plants possess a rosette of
leaves close to the ground : these leaves are mostly simple and
COMMON BIRD'S-FOOT TREFOIL 441
ovate with long petioles. Subsequently branches are produced in
the axils of the radical leaves, and upon them are borne pinnatifid
or compound pinnate leaves, each with a large terminal lobe.
The inflorescences are dense heads of yellow flowers, the
calyces of which are inflated and covered with long downy
hairs. The andrcecium of the flower is monadelphous, the
gynaecium stalked, containing two ovules.
The ripe fruit is a flattened legume and contains a small seed,
one half of which is yellow, the other half bright pale green.
The kidney vetch is a useful plant sown alone for sheep food
upon calcareous or marshy soils too poor to grow anything else.
It is capable of resisting prolonged drought, and makes nutritious
hay although it is scarcely suited to this purpose on account of
the procumbent character of the stems, much of which escapes
the scythe.
Seed is sown in spring in drills 12 or 14 inches apart, at the
rate of 17 Ibs. per acre.
In mixtures, either for long or short leys on dry ground, the
kidney vetch is worthy of a place both on account of its nutritive
quality and its permanence.
Bird's-foot Trefoils (Genus Lotus).
ai. Common Bird's-foot Trefoil (Lotus corniculatus L.). An
herbaceous perennial common in dry pastures. From the
short thick rhizome spreading decumbent stems arise, each of
which is from 4 to 16 inches long. The leaves are pinnately
compound with five leaflets; the lowest pair of the latter are
separated considerably from the three upper ones, and resemble
the stipules of a trifoliate leaf, so much so that at first sight the
leaf appears to be trifoliate and not pinnate : hence the name
of trefoil.
The flowers, five to ten in number, are arranged in umbel-
like cymes at the end of long slender axillary peduncles.
The corolla of the flower is bright yellow, the 'standard*
being frequently tinged with deep orange or red. The fruit is
442 LEGUMINOS^E
a long slender legume purplish red in colour; within it are a
number of small brown roundish-oval seeds, partially separated
from each other by transverse false partitions.
Bird's-foot trefoil is a nutritious plant much liked in a young
state by all kinds of stock. It is not very productive, but on
account of its good quality and permanence is a leguminous
plant worthy of inclusion in permanent grass mixtures for the
lighter classes of soil. Unfortunately genuine seed is expensive
and liable to be adulterated with its allied species, Greater or
Marsh Bird's-foot Trefoil (Lotus uliginosus Schk. = Z. major
Sm.) (see p. 663), which is a native of damp meadows, and only
of agricultural value for use on marshy ground.
Bird's-foot trefoil is a very variable plant in habit of growth,
and size of stem, leaves, and flowers : some varieties are smooth
while others are hairy.
Gorse (Genus Ulex).
22. Gorse, Furze, or Whin (Ulex europaus L.). A perennial
bushy shrub growing from 2 to 5 feet high, and frequent on
heaths and dry commons throughout the country.
The first foliage-leaves appearing after the cotyledons are
trifoliate like those of clover, but with smaller rounded leaflets,
On the older parts of the plant the leaves are very narrow, about
a quarter of an inch long, and end in short, soft spines ; in
their axils arise rigid furrowed branches which end in stiff spines.
The flower is solitary and axillary, with yellow corolla, a
deeply two-cleft calyx : the andrcecium is monadelphous.
The fruit is a two-valved legume, slightly longer than the calyx,
and containing two or three seeds.
A small variety of this plant, named Ulex strictus Mackay,
is met with in parts of Ireland; it has soft, spiny branches,
but does not come true from seed.
Two other British species of Ulex are known, but they are
of no practical importance.
WHITE LUPIN 443
Common gorse is cultivated in some districts upon thin,
apparently sterile sandy soils, and utilised as food for horses
and cows in winter. It forms very nutritious fodder, and cows
are said to give a better yield of milk when fed with gorse than
when they are given good meadow hay ; moreover, the milk is
of rich quality.
Before being fed to stock, the stiff spiny branches of the
plant are generally crushed between rollers or otherwise bruised
and softened by special simple machinery.
The. seed is drilled in rows 10 to 18 inches apart in April or
May on clean ground at the rate of 10 to 15 Ibs. per acre.
The young plants are slow in growth, and the first cut is
taken in the second year. After being established the crop is
cut chiefly in winter and spring when green food is scarce.
In some districts an annual cut is taken, while in others the crop
is cut once every two years ; in the latter case alternate rows are cut.
Dyer's Greenweed or Woad-wax (Genus Genista).
To this genus belongs Dyer's Greenweed (Genista tinctoria L.),
a shrubby leguminous weed of stiff clay soils (p. 614).
Best-harrow (Genus Ononis).
23. To this genus belongs Rest-harrow (Ononis spinosa L.), a
shrubby weed common in many districts, and difficult to exter-
minate on account of its deeply-penetrating roots (see p. 6 1^5).
Lupins (Genus Lupinus).
24. The genus Lupinus includes a large number of species of herb-
aceous and half shrubby plants many of which are grown in gardens
for their handsome spikes or heads of brightly-coloured flowers.
Several annual species are cultivated on the Continent as farm
crops for * green manuring/ the chief of these being Yellow
Lupin {Lupinus luteus L.), and in lesser degree Blue Lupin (Z.
angustifolius L.) and White Lupin (L. albus L.).
All the species are exceptionally rich in nitrogenous constitu-
ents and grow on poor sandy soils, which they enrich enormously
when ploughed in.
444 LEGUMINOS^E
Many sandy districts on the Continent which were practically
valueless have been very materially improved in fertility by the
utilisation of these plants as ' green manure.'
Lupins contain a greater amount of digestible albuminoids
than any other known crop, and besides their use as a manure
are also used in a green state folded off by sheep; they are
occasionally made into hay. The plants contain a variable
proportion of a bitter alkaloid which makes them unpalatable to
horses and cattle, and sheep at first appear to dislike the crop.
In addition to the bitter alkaloid, lupins under certain
indefinite conditions of soil, manuring, and storage sometimes
contain a poisonous compound named lupinotoxine, which
rapidly produces fatal results in sheep when the latter are fed
with even moderate amounts of the cut green fodder or hay.
Of the various methods to render the lupin crop perfectly
innocuous, heating with steam under pressure of one or two
atmospheres has proved the most certain.
Lupins succeed best on dry sands or light sandy loams. On
light calcareous ground they do not grow satisfactorily ; even on
sand resting on a chalky subsoil they often fail. Stagnant water
in the subsoil or an excess of humus in the soil is also detri-
mental to their development.
In the early stages of growth the tap root develops extensively
while the parts above ground grow very slowly.
25. Yellow Lupin (Lupinus luteus L.). This species is the
one most generally grown as a farm crop. It is an annual, with
erect hairy stem from 2 to 3 feet high. The leaves are palmately
compound with from seven to nine lanceolate leaflets.
The inflorescences are loose pyramidal heads consisting of
several (five to twelve) whorls of bright yellow papilionaceous
flowers*
The ripe legumes contain three or four seeds and are from
i \ to 2 inches long ; they appear swollen at the seeds, and the
valves are woolly on the outside.
WHITE LUPIN 445
Each seed is roundish kidney-shaped about the size of a pea,
of whitish colour flecked with black spots and small streaks.
The seeds are drilled in rows from 9 to 15 inches apart on a
clean seed-bed in May or June; i to 2 bushels per acre are
needed.
26. Blue Lupin (Lupinus angustifolius L.) is an annual with
taller stems, more woody than those of the yellow species, and
hence not so suitable for fodder ; the leaflets are narrow and the
flower spikes have fewer flowers and these are blue in colour.
The seeds are rough, about the size of a small bean seed and
generally buff coloured flecked with rusty spots.
The White Lupin (Lupinus albus L.) is a South European
species grown extensively in warmer parts of France, Spain
and Italy for green manuring and for its seeds, which are used as
food after the bitterness has been removed from them by steeping
in water ; it requires a hot climate to ripen its seeds properly.
Ex. 228. The student should examine all the leguminous plants mentioned
which have not previously been dealt with in order to become practically
acquainted with the peculiarities of each species. Make a point of watching
their development as far as possible, and compare their flowers .fruits and seeds.
SUMMARY OF THE GENERIC CHARACTERS OF LEGUMINOUS
FARM-PLANTS.
1. Leaves pinnate, ending in tendrils (Fig. 33), except in the bean the
petiole of the leaf of which ends in a short bent point. Andrcecium di-
adelphous : legume two-valved, dehiscent.
a. Free end of staminal tube cut off at right angles to its length ; style,
threadlike. Genus Vicia (Vetches and Bean).
h Free end of staminal tube cut off obliquely ; style flattened.
(i) Style not grooved, Genus Lathyrus (Everlasting Fea).
(ii) Style grooved, Genus Pisum (Garden and Field Pea).
2. Leaves pinnate, with two or more pairs of opposite and one single
terminal leaflet.
a. Andrcecium diadelphous.
Fruit indehiscent, but split transversely into one-seeded nut-like
joints (a lomentum). Genus Ornithopus (Serradella).
Fruit a one-seeded nut Genus Onobrychis (Sainfoin).
Fruit a long two-valved dehiscent legume.
Genus Lotus (Bird's-foot Trefoil).
446 LEGUMINOS^E
b. Androecium monadelphous (in the single British species).
Calyx inflated ; fruit a one-seeded nut.
Genus Anthyllis (Kidney- Vetch).
3. Leaves with three leaflets.
a. Androecium diadelphous.
(i) Flowers in a dense head.
Faded corolla encloses the fruit. Genus 7*rifolium (Clovers).
Faded corolla drops away from the fruit ; legumes curved or spirally
twisted. Genus Medicago (Lucerne and Yellow Trefoil),
ii) Flowers in open elongated racemes.
Fruit short, indehiscent, with one to three seeds.
Genus Melilotus (Melilot).
J. Androecium monadelphous. Genus Ononis (Rest Harrow).
4. Leaves simple.
(i) Leaves spinous.
Calyx deeply two-lipped. Genus Ulex (Gone),
(ii) Leaves flat.
Calyx shortly two- lipped. Genus Genista (Dyer's Weed).
5. Leaves digitate with more than three leaflets.
Genus Lupinus (Lupin).
CHAPTER XXXII.
UMBELLIFERJE.
i. General characters of the Order. Inflorescence generally
a compound umbel ; flowers small, bisexual, usually regular and
epigynous. The outer flowers of the compound umbel are often
irregular and zygomorphic, the petals directed outwards being
larger than those pointing inwards.
Calyx superior, often absent ; when present it generally con-
sists of five minute tooth-like projections. Corolla polypetalous,
five petals, obcordate or obovate, usually curved inwards at the
free tip, mostly white, yellow, or pink. Androecium of five
stamens curved inwards in the young flower. Gynaecium in-
ferior, syncarpous, two carpels ; each carpel contains one pendul-
ous ovule. The ovary bears on its summit a fleshy swollen
nectary termed the stylopodium (d t Fig. 134). From the stylo-
podium arise two styles, which are often slightly curved outwards.
The line of union of the two carpels is known as the commissure
(c, D, Fig. 134). Each carpel frequently bears on its outer or
dorsal surface nine more or less well-marked raised lines or
ridges. Five of them are described as primary ridges ; two of
these, the marginal ones, are close to the commissure, the other
three, dorsal ridges, being regularly placed on the back or dorsal
part of the carpel (Z>, Fig. 134). Sometimes occupying the
spaces intermediate between these five ridges are four secondary
ridges, which are occasionally as prominent or more so than the
primary ones; they are, however, often missing or but feebly
developed.
r 447
448
UMBEL-LIFERS
The ridges may be continuous simple raised lines or may
consist of lines of prickly, hairy, or knob-like projections.
In the wall of the ovary are longitudinal canals termed vitta,
which most frequently are present in the substance of the furrows
between the primary ridges (#, Fig. 134), and when the fruit is
ripe can often be seen as dark brown or black lines on the peri-
carp wall. They contain secretions of volatile oils, balsams, and
gum-resins, which generally give to the fruit its peculiar odour
and taste; the characteristic taste of caraway, coriander, and
other similar fruits of the Umbelliferse is due to essential oils in
their vittae
FiG. H4. A, Fruit of Wild Chervil (Chtfrophyllum sylvestre L.).
B, The same later, showing the manner of splitting, c carpophore ; m mericarps; d
stylopodium.
C, Transverse section of A. x Commissure ; v vittae ; e endosperm of the seed.
D % Transverse section of the ovary of Fennel (F&niculum officinale All.), p Primary
ridges ; v vitta; ; c commissure.
The number and arrangement of the ridges and vittse are best
seen when the ovary is cut transversely.
The fruit is a schizocarp which divides into two mericarps ;
each of the latter is a closed carpel containing a single endo-
spermous seed. When the fruit is ripe the mericarps separate
from each other and remain suspended on a thin, usually divided,
extension of the flower axis, termed the carpophore (c, B>
Fig. 134).
The seed is endospermous and generally united with the inner
wall of the pericarp. The endosperm contains a considerable
proportion of oil and no starch. The embryo is small, embedded
PARSNIP 449
in the endosperm in the part of the seed nearest to the apex of
the fruit.
The flowers are generally pollinated by small insects, which
easily obtain the exposed nectar secreted by the stylopodium.
Protandrous dichogamy is common ; the stamens often set free
their pollen and wither up before the stigmas are developed.
2. The Umbellifera is an Order comprising about 1300
species of plants, generally herbaceous, and most largely repre-
sented in temperate regions.
The stems are frequently hollow. The leaves are alternate,
their blades usually very much divided in a pinnate manner,
and the petioles often very broad and inflated, forming a sheath
which partially clasps the stem.
There is a great similarity among many of the species and
genera of the Order, and only careful attention to details of the
form of the fruit, its ridges and vittae, and the presence or
absence of involucres below the umbels and umbellules will
enable a student accurately to distinguish the various species he
may meet with.
A common characteristic of umbelliferous plants is the pos-
session of secretory canals, which become filled with essential
oils, balsams, or gum-resins. These canals are not only met
with in the pericarp of the fruit but are frequently present in the
stems, roots, and leaves, and it is from the substances secreted
in these canals that many of the plants derive their strong
aromatic odour and taste.
Many of the representatives of the Order, such as hemlock and
cow-bane, contain poisonous alkaloids ; the dangerous compounds
are not present in any special canals or ducts, but are common
in the cell-sap of all parts of the plants, but sometimes more
especially present in their stems, leaves, or roots.
The only plants cultivated on the farm belonging to the Urn-
belliferae are the Carrot (Daucus Carota L.) and Parsnip (Peuce-
danum sativum Benth.). Besides the above those common in
450 UMBELLIFEIUE
gardens also included in this order are Celery (Apium graveolens
L.), Parsley (Carum Petroselinum Benth.), and Caraway (Carum
Carui L.).
A number of species of Umbelliferae are important on account
of their poisonous qualities ; the chief ones are mentioned later.
A few are weeds of the farm, but practically none of these need
serious attention.
3. Wild Carrot (Daucus CarotaL,.). A well-known plant com-
mon in dry pastures and on roadsides throughout the country. It
most frequently behaves as an annual, though it is occasionally
biennial. With the exception of its root, which is comparatively
thin and woody, it resembles the cultivated forms in stem, leaf,
flower, and fruit.
The wild carrot affords one of the best examples of the
possibility of rapid modification of plants by special selection
and improved cultivation. M. Vilmorin raised passable garden
varieties with thick fleshy ' roots ' and of biennial habit in four
generations from the wild species, and there is no doubt that all
the cultivated forms of carrot have been derived from the same
source.
4. Cultivated Carrot.
SEED AND GERMINATION. The so-called carrot 'seed 1 used
for raising a crop consists of the mericarps of the fruit (see
below).
The young seedling possesses two long narrow cotyledons, a
well-marked hypocotyl which at first grows above ground, and a
slender primary tap root (i, Fig. 135). The hypocotyl and root are
quite distinct from each other in colour and general appearance
in the early stages of growth.
ROOT AND HYPOCOTYL. Without going into the internal ana-
tomy it is always possible in very young seedlings to distinguish
these two parts of the plant.
The hypocotyl is free from roots, but the primary root bears a
number of secondary ones chiefly in four longitudinal rows.
CULTIVATED CARROT
451
After a time it is noticed that in many cultivated forms, and
especially those grown in gardens, the hypocotyl, which is at
FIG. 135. Carrot seedlings at four successive stages of growth, a Hypocotyl ; b cotyledon ;
c root ; d first foliage-leaf.
first above ground, becomes gradually drawn below the surface
by the contraction of the root ; the hypocotyl itself sometimes
452 UMBELLIFEIUB
contracts also and the cotyledons, which were originally some
distance above the soil, now lie close upon it
Soon thickening commences, both in the primary root and hypo-
cotyl, and as adventitious roots make their appearance from the
internal tissues of the latter, the distinction between the stem and
the true primary root becomes rapidly obliterated so far as external
appearances are concerned. In some field carrots a good deal of
the hypocotyl continues to grow above ground, thus resembling
mangels and turnips.
On good soils the primary root extends to a considerable depth,
but only the upper portion of it becomes thickened ; the lower
part, which is left in the ground when the 'carrot 1 is pulled or
dug up, is long, thin, and cord-like, and bears many fine branch-
ing rootlets.
As in the case of all fleshy farm ' roots,' except kohl-rabi, the
'root 1 of the carrot, for which the plant is cultivated, consists of
hypocotyl and root combined, the relative amount of each vary-
ing in different * races ' or ' strains * of the plant.
On the outside of the 'carrot* are seen delicate secondary
roots which are arranged in four longitudinal rows ; but on account
of irregular growth the rows do not always remain straight
The thickened fleshy 'root* of the carrot, like that of the
turnip, presents the same general arrangement of tissues as is
met with in ordinary typical dicotyledonous roots and stems:
the differences consist in the abnormal development of the
elements composing its tissues.
A transverse section of a carrot (2, Fig. 136) shows a layer
consisting of parenchymatous bast and secondary cortex (</),
which is wide in comparison with that of the turnip 'root/ and
of red or scarlet hue in red varieties. In the centre is the
1 core ' of wood (a), generally yellowish or dull white in colour.
The relative proportion of wood to bast varies in different
'races' of carrots; the endeavour of the plant breeder is to
obtain a relatively wide cylinder of bast (d) and a small core,
CULTIVATED CARROT
453
as it is in the former that the greatest amount of sugar and
other nutrient materials is stored.
The wood in the first season of growth contains no fibres or
fibrous cells, but consists mainly of thin walled unlignified
vessels and delicate wide-ceiled wood-parenchyma. Narrow
medullary rays are visible. In the second season and in
Bolted' carrots which have run to
seed in the first season, the wood last
produced by the cambium-ring (c) be-
comes strongly lignified and fibrous by
the time that flowering commences.
STEM AND LEAVES. During the first
season of growth the carrot stores up
reserve food in its thickened root and
hypocotyl; the epicotyledonary por-
tion of the stem remains short until
the second season, when the terminal
1.
FlG. 136. d) Longitudinal ; (2) transverse section of carrot 'root, 1 showing disposition
of tissues, d Thin -walled parenchymatous bast and secondary cortex ; a. wood ('core')*
t cambium-ring ', r secondary root.
bud sends forth a furrowed, somewhat bristly, solid stem 2 or
3 feet high with spreading branches.
The radical leaves have long petioles ; all are bipinnate with
deeply pinnatisect leaflets, the ultimate segments being small
and narrow.
INFLORESCENCE AND FLOWERS, The inflorescence is a com-
3i
454
UMBELLIFER^E
pound umbel: the bracts 'of the involucre extend as far as or
beyond the flowers, and are pinnatifid, the segments very narrow
ind acuminate. The umbellules have involucels of narrow,
3r pinnatifid bracteoles.
After flowering the outermost main branches of the compound
jmbel curve inwards, and the whole inflorescence then forms a
lollow cup or nest-like structure.
The flowers (i, Fig. 137) are epigynous : the calyx superior, con-
sisting of five short tooth-like sepals : the corolla is composed of
ive white incurved petals alternating with the sepals (the petals
rf the central flower of the umbel are often pink or reddish) ; the
5
1.
3.
FIG. 137 i. Flower of Carrot (Daucus Carota. L.). c Minute sepal of calyx ;/ petal ;
ovary ; st withered stamen ; ^stylopodium ; s style and stigma.
2. Fruit of Carrot. The ovary is covered with long spines and hairs, d Stylopodium ;
style and stigma.
3. Transverse section (magnified) of ovary through line A, B,d (2). / Primary ridges ;
secondary ridges ; v vittae ; rb vascular bundles ; cm embyro of seed ; e endosperm.
mdroecium possesses five stamens, which set free their pollen
tnd fa 1 ! away soon after the flower opens \ the gynsecium is
nferior and syncarpous, consisting of two united carpels; the
ipper part of the ovary has a white fleshy stylopodium which
:>ears two curved styles.
The four secondary ridges on each carpel are more prominent
,han the primary ones, and bear ten or twelve long spinous pro-
ections, on the end of which are three or four slightly hooked
RED ALTRINGHAM 455
hairs: the five primary ridges (/>, 3, Fig. 137) bear long uni-
cellular hairs.
THE FRUIT AND SEED. The fruit is a schizocarp. Upon the
two dry mericarps the spiny secondary ridges are conspicuous, of
light brown tint. It is on account of these spiny projections that
the mericarps cling together and prevent the * seed ' from being
sown evenly without previous rubbing and mixing with sand or
dry ashes.
Each mericarp contains a single endospermous seed, with a
minute dicotyledonous embryo.
Within the wall of the pericarp in each secondary ridge is one,
rarely two, vittse (3, Fig. 137, v), containing an oil which gives the
ripened mericarps a characteristic odour most easily recognised
when the latter'are rubbed vigorously in the hands.
VARIETIES. Carrots vary much in the length, rapidity of
growth, and colour of their * roots/
They also differ in their feeding-value, and the proportion of
' rind ' to ' core. 1 Moreover, some varieties grow with a consider-
able proportion of their thickened * root ' (hypocotyl) above
ground, while others have their * roots' entirely buried in the
ground.
Of all varieties the White Belgian gives the largest crop. The
upper part of the * root ' is pale dull green, the lower part and
flesh white. The * roots' are of moderate length, very thick,
and grow with the upper parts about 6 inches above the ground :
from to | of the white root is below ground. It is a hardy variety
adapted to almost all soils. The feeding-quality is low compared
with the red varieties.
Of slightly superior quality, but smaller yielding capacity, is the
Yellow Belgian, with yellow flesh, but otherwise resembling the
white variety.
Of red varieties the best cropper is Red Altringham. It
possesses thick long roots ending somewhat abruptly : the upper
part grows slightly above ground and is of greenish-purple
456 UMBELLIFER>E
colour; the rind is pale orange-red, the rather small core
is yellow. It needs good deep soil for proper growth and is
superior in feeding value to the White Belgian variety.
For growth upon shallower soils the * Scarlet Intermediate '
Varieties are best. They are very thick, usually only about
two-thirds the length of the Red Altringham, and of excellent
feeding-quality. Some of them are adapted for market-garden
purposes.
Long Bed Surrey is a variety with tapering roots of great
length in proportion to their thickness ; the rind is deep red, core
yellowish. For field cultivation it is not so good as Altringham.
SOIL. Stiff soils and those which are very shallow are unsuited
to this crop.
The long varieties of carrots require a deep well-pulverised
sandy loam : on shallow soils, especially where the subsoil is
stony or imperfectly broken up, the deep-growing varieties
lose their symmetrical shape and become irregular, 4 fanged ' or
'forked/ some of the secondary roots becoming thickened as
well as the main primary root. To some extent the variety can
be adapted to the character of the soil ; a few of the short thick
kinds sometimes produce a fair crop on comparatively shallow
soil
SOWING. The 'seed' of the carrot germinates somewhat
slowly, and the young plants on account of their small narrow
leaves are liable to be smothered by annual weeds. To avoid
this it is advisable to damp the ' seed ' and allow it to remain in
a small heap for seven or eight days until signs of germination are
apparent before drilling. The ' seed ' is best mixed and rubbed
with dry sand or ashes previous to sowing. The crop is gener-
ally drilled in rows from 1 8 to 24 inches apart, on well-cleaned
and finely pulverised soil. The superabundant young plants are
subsequently hoed out, and the remainder singled and left about 6
or 7 inches apart. From the beginning to the end of April is the
best time for sowing ; earlier than this the temperature is too low
LONG RED SURREY 457
to promote vigorous growth of the carrot and the plants are liable
to be smothered by annual weeds if germination and active
growth is delayed.
The amount of good, new, well-cleaned seed necessary for one
acre is 4 or 5 Ibs.
YIELD. The average yield varies from 10 to 20 tons per acre
according to the variety grown.
The White Belgian variety occasionally gives a crop of 30
tons per acre.
COMPOSITION. In a wild state the carrot stores up starch in its
' roots,* the cultivated forms however rarely or never store this
carbohydrate in them, its place being taken by sugar.
The amount of water in White Belgian carrots is on an average
about 88 per cent.; the red varieties contain from 86 to 87 per
cent. The soluble carbohydrates, of which the greatest propor-
tion is sugar, averages 9*2 per cent., the nitrogenous substances
generally reach 1*2 per cent, of which a little more than half are
albuminoids. The ' fibre ' is rather high, namely 1*3 per cent.
With the exception of parsnips and potatoes, red carrots con-
tain more nutritious dry matter per ton than any other root crop
ordinarily grown as food for stock : the leaves or ' tops ' are
excellent, as well as the ' roots.'
Ex. 229. Examine the commercial 'seeds' of the carrot. Note the
secondary ridges of spines. How many ridges are there on each ? Cut thin
transverse sections of the mericarp and examine them for the vittse.
Note the odour when the * seeds ' are rubbed in the hands.
Ex. 230. Raise carrot seedlings in damp sand 01 sandy soil, and note the
length and shape of the cotyledons, hypocotyl, and primary root. Observe
the amount of hypocotyl above ground in a bed of seedling carrots in the
garden and watch the withdrawal of the hypocotyl into the ground as tht
plants increase in age.
Ex. 231. Carefully dig up a half-grown carrot, taking care to go deep
enough to obtain the fine extension of the tap root, and also the secondary
roots. Wash away the earth carefully and examine the extent, thickness,
and position of the lateral roots
458 UMBELLIFER^E
Ex. 232. Cut longitudinal and transverse sections of an old carrot. Note
the colour, thickness and texture of the various parts. Observe that the
lateral roots run through the orange parenchymatous bast and secondary
cortex.
Ex. 233. Examine the stem, branches, leaves, and inflorescences of a
'bolted carrot,' or the same parts in a wild carrot.
Ex. 234. Examine and describe individual flowers of the compound umbel
of a carrot. Observe the colour of the flower in the centre of each compound
umbel.
Note the ovary and its two united carpels. Cut sections of young fruits
and examine them with the microscope.
Ex. 235. Obtain as many kinds of 'carrots' as possible. Note their
colour, shape, length, and proportion of ' rind ' to ' core ' when cut across.
5. Parsnip (Peucedanum sativum "Renth. Pastinaca
A wild annual or biennial plant occurring on roadsides and
waste places, especially on calcareous soils. Like the wild carrot
this plant is very easily modified by cultivation, and all the field
and garden parsnips have undoubtedly arisen from the common
wild species.
The cultivated forms differ from the wild plant chiefly in the
thickness of the root ; the leaves and stems are generally less
hairy than the wild parsnip, but in other respects there is no
difference between the two.
SEED AND GERMINATION. The 'seeds' sown fora crop are
thin flat mericarps of the fruit, each of which contains a single
true endospermous seed.
The seedling has two narrow cotyledons and its first foliage-
leaves are cordate or palmately three-lobed with coarsely serrate
margins.
ROOT AND HYPOCOTVL. These parts of the plant resemble
those of the carrot.
STEM AND LEAVES. The flowering stem sent up in the
second season of growth is stout, with deep longitudinal furrows.
It is hollow and grows to a height of 2 or 3 feet.
The leaves are oblong, pinnate, with two to five pairs of
leaflets each from i to 3 inches long, ovate, with deeply
* HOLLOW CROWN ' 459
serrate margins ; the terminal leaflet is three-lobed. The upper
surfaces of the leaflets are smooth, the lower surfaces soft and
hairy.
INFLORESCENCE AND FLOWERS. The inflorescence is a com-
pound umbel without bracts or bracteoles. The flowers are
epigynous : calyx superior, of five very small teeth ; corolla of
five small, bright yellow incurved petals : androecium of five
stamens : gynaecium syncarpous, of two carpels, dorsally com-
pressed with a broad commissure : each carpel has five primary
ridges, the two marginal ones forming wing-like projections.
FRUIT. The fruit is a dorsally compressed schizocarp ; the
mericarps are thin and flat, of oval or circular outline, six dark
brown vittse reaching not quite to the base, are visible on
each, four on the dorsal, and two on the inner (commissure)
side. The fruit has a divided carpophore. Within each mericarp
is a single flat, endospermous olive-green seed.
VARIETIES. There are comparatively few varieties of this
1 root.' Those cultivated as food for cattle are generally long-
rooted varieties resembling the long carrots in shape.
The only two common varieties are (i) the Large Cattle
Parsnip, which has the upper part of the * root ' rounded or con-
vex, and (2) the * Hollow Crown,' which has a slightly shorter
and thicker depressed or concave ' top*.
A form met with in gardens having a relatively very short
thick 'root' is known as the 'Turnip-rooted' parsnip.
SOIL, CULTIVATION AND SOWING. Parsnips can be grown on
soil usually too stiff for a good crop of carrots, but the cultivation
and general management needed for the latter is appropriate for
the parsnip.
The ' seed ' is best sown in March, an earlier date than that
adapted to the carrot, at the rate of about 6 or 7 Ibs. per acre.
Less seed would suffice if new, but commercial samples are
usually very poor in germinating capacity and nearly always
mixed with old dead seed.
460 UMBELLIFER>
The drills are drawn about 15 inches apart, and the plants
eventually singled out to a distance of 6 or 7 inches asunder.
The average yield of ' roots ' per acre is about 1 1 tons.
COMPOSITION. The parsnip properly grown contains less water
than the carrot, and is the most nutritious of ordinary ' root f
crops. The amount of water appears to average about 83 per
cent : starch is present in small quantity, but the chief useful
carbohydrate is sugar.
Ex. 236. Carry out experiments and observations upon the parsnip similar
to those mentioned for the carrot on pp. 457, 458.
The poisonous Umbelliferae, with which it is desirable that the
student of agriculture should be acquainted, are the following :
6. Hemlock (Conium maculatum L.). A common biennial
plant, generally 2 to 3 feet high, occurring in hedges, fields, and
waste places in many parts of the country. The stem is smooth,
hollow, of dull green colour with a thin grey bloom upon it, and
spotted with small brownish-purple blotches. The leaves are
large tripinnate, with lanceolate pinnatifid leaflets: they are
of peculiar dark glossy-green tint. The compound umbels of
white flowers possess both bracts and bracteoles.
The fruit is oval or round; each mericarp possesses five
characteristic knotted primary ridges.
The whole plant has a foetid smell, and is excessively poison-
ous. Its dangerous qualities are due to the presence of several
narcotic alkaloids which are met with in greatest abundance in
the leaves, young shoots, and fully-developed green fruits ; the
chief of these poisonous compounds is conine.
7. Water Hemlock or Cow-bane (Cicuta virosa L.). A some-
what uncommon tall perennial met with in ditches and by the
side of rivers. The flowers are white and the stem from 3 to 4
feet high, thick and furrowed ; its leaves are large, twice or thrice
pinnate, the leaflets about 2 or 3 inches long and lanceolate,
with serrate margins. Cows are sometimes poisoned by eating
it, hence its name.
FOOL'S PARSLEY 461
8. Water Dropwort (Oenanthe crocata L.). A tall perennial
resembling celery and sometimes mistaken for it with fatal
results. It grows in situations similar to those suited to wild
celery, namely, near rivers and ditches. The flowers are pale
yellow, and the juice squeezed from the plant is yellow, and
stains the skin.
9. Poors Parsley (Atthusa Cynapium L.). A common annual
weed of cultivated ground, both gardens and fields. Its stem is
slightly furrowed and generally about a foot high. The leaves
are bipinnate, smooth and shining, of dark green colour, and
when bruised have a strong stinking odour. The flowers are
white, and the small umbels have involucels of three or four long,
narrow, slender bracteoles which point outwards and downwards.
By the smell and the conspicuous bracteoles the plant is readily
distinguished from others of similar general appearance. It has
occasionally been mistaken for parsley with bad effect, but
rarely, if ever, led to fatal results.
Ex. 237. The student should examine the roots, stems, leaves, inflor-
escences, and fruits of as many common wild umbel lifers as possible. He
should also become especially acquainted with the botanical characters of
the poisonous species just mentioned
CHAPTER XXXIII.
SOLANACE^E.
1. General Characters of the Order. Herbs or shrubs,
Leaves usually alternate, exstipulate. Flowers generally regular,
hypogynous. Calyx, inferior gamosepalous, 5-fid, persistent.
Corolla hypogynous, gamopetalous, 5-lobed, usually campanu-
late or salver-shaped.
Andrcecium of 5 epipetalous stamens. Gynaecium syncarpous,
2 carpels ; ovary usually 2-celled with many ovules on a thick
axile placenta. Fruit a capsule or berry ; seed endospermous.
An extensive Order of plants, chiefly found in the tropics and
especially in South America, Poisonous alkaloids occur in
many plants belonging to the Order.
The genus Solanum, from which the Order is named, embraces
about 800 or 900 species, many of them ornamental plants.
Only five or six species bear tubers, the chief being the common
potato.
2. Potato (Solatium tuberosum L.). Introduced into Europe
in the sixteenth century, first into Italy and Spain, and indepen-
dently into the British Isles a little later in the same century.
SEED AND SEEDLING. The endospermous seed germinates
readily and produces a young seedling with well-marked primary
root and two ovate cotyledons (4, Fig. 138). The plumule
develops intp an upright stem with leaves, and from the axils
of the cotyledons, whose petioles lengthen considerably, shoots
arise which are positively geotropic (Fig. 140). These shoots
soon find their way into the ground, and after the growth of two
or three intcrnodes their tips become tuberous (</, Fig. 141)
462
POTATO
463
through the deposition within them of reserve foods, the chief
of which is starch. Similar tube-bearing shoots may also arise
from buds in the axils of the foliage leaves above the cotyledons.
The thin part of the underground rhizomes bear scale-like
leaves, and these are also present on the young tubers, but
eventually shrivel up before the latter are ripe. Usually only
FIG. 138.
1. Potato seed germinating.
2. Section through the same, showing position
of cotyledons and endosperm (shaded).
3. Seedling nearly free fiom seed-coat.
4. Seedling quite free (10 days 1 old); a hypo-
cotyl ; b root ; c cotyledons.
FIG. 139.
Potato seedling (16
days old), later stage of 4,
in previous Fig., showing
plumule f. The coty-
ledons c have become
broader ; a hypocotyl ;
b root. (Natural size.)
one tuber is developed at the end of a rhizome in seedling
plants. Sometimes, however, lateral branches which bear
tubers are produced from the axils of the scaly leaves of the
rhizomes.
At the end of the growing season the stems and leaves above
464
SOLANACE^E
ground and the thin parts of the underground stems die ; the
tubers remain dormant below during winter, and in the following
spring germinate and send forth new shoots from their ' eyes.'
The tubers from a one-year-old plant are small, often not
larger than a broad bean, and it is only after three or four years
growth that they reach the size of ordinary potatoes.
FIG. 140.
Potato seedling (26 days' old), later stage
of Fig. 139 The Plumule * has developed
considerably, and in the axils of the coty-
ledons two shoots d have been produced.
a hyp^cotyl; b root; c cotyledons; e
epicotyl ; x ground-line (Natural size).
FIG. 141.
Potato seedling (jo weeks' old), later
stage of Fig. 140. The shoots d have
now pushed their way below ground and
at their tips small tubers have formed.
(Natural size)
ROOT. The roots of the potato plant extend themselves
chiefly in the upper layers of the soil, and are fibrous and
copiously branched. The primary root and its branches are
distinct from the tuber-bearing rhizomes (Fig. 141), but from the
nodes of all the stems below ground adventitious roots arise in
POTATO 465
abundance. The extensive development of the latter depends
upon the presence of moist air; in dry air they do not
appear.
The tubers themselves never bear roots, and are, therefore,
unlike the Jerusalem artichoke tubers in this respect.
STEM AND TUBER. The stems are herbaceous; two forms
are present upon the potato plant, namely, the upright stem
above ground and the horizontal rhizome below.
Although their geotropic behaviour is not the same, they are
essentially the same in structure ; the rhizome can be changed
into an ordinary shoot with green foliage-leaves by bringing it
above ground.
The rhizome is usually not more than from i to 3 inches long
in early varieties, and the tubers consequently appear heaped up
round the stem when dug. Those giving heavier crops have
longer and more branched rhizomes, while varieties with very
long rhizomes usually give an unsatisfactory yield, although
individual tubers may reach a large size.
Leafy stems resembling that from which Fig. 142 was drawn,
and showing tuber development in the axils, are readily produced
by allowing old tubers to germinate in spring in a darkened cellar
kept somewhat damp. Moreover, if the potatoes are picked
off below ground as fast as they form, the plant develops tubers
in the axils of the leaves above ground.
The first internodes of the rhizome below ground are of con-
siderable length ; those produced later at its tip remain shorter,
but increase in thickness rapidly, and form a tuber.
TUBER. That the potatoes are thickened pieces of stems is
seen from a study of their origin ; the rhizomes, of which they
are merely the ends, arise in a normal manner in the axils of
leaves below the soil and although they occur under ground,
they have no connection with the root-system of the plant.
A well-grown tuber usually shows at its base or c heel ' a piece
of the withered rhizome, and on its surface many * eyes ' which
466
SOLANACE^E
are arranged spirally. At the * rose ' end, or the morphological
apex of the tuber, the * eyes ' are more crowded together than at
its c heel ' or base, the older
internodes being longer than
the younger ones. Each 'eye '
appears as a collection of buds
lying more or less in a de-
pression ; the latter is the
axil of a scaly leaf which was
visible when the tuber was
young, but now withered up
and lost. The number of
buds in each ' eye ' may be as
many as twenty, but three is
the usual number.
In reality the ' eye ' is a
lateral branch with unde-
FIG. 142. Leafy stem of potato, showing tuber , , . . , , .
growing in the axiU of an ordinary leaf a Tuber VelOped intemodeS, the Whole
Mrtoftr: tuber being generally a richly
branched shoot-system and
not a simple shoot.
Tubers are not always of the same form ; three moderately
distinct and fairly constant types are prevalent, namely, (i)
'round,' (2) l oval] and (3) 'kidney' shapes. The round
type is somewhat spherical, and has fewer internodes and ' eyes'
than (2) and (3), both of which are elongated. The kidney
potatoes are thickest at the ' rose ' end and taper towards the
' heel/ while the oval varieties are thickest in the middle and
taper towards both ends. Those differences are sufficiently
marked and constant to form a basis of classification of the
varieties in cultivation.
In some instances the tubers are of very irregular shape.
When long-continued dry weather checks vegetation, and is
followed by rains, the partially-ripened tubers, instead of
,ub e rina x ,iofieaf,.
POTATO 467
increasing regularly in thickness when active growth begins
again, grow out from the ends or about the lateral 'eyes.' The
new growths may form irregular lumps or even smaller tubers on
the older ones; this is known as super-tuberation or second
growth, and is most common in kidney and oval varieties.
The anatomy of the tuber in its young state resembles that of
the rhizome, to which it belongs, and like all similar stems
possesses epidermis, cortex, and vascular cylinder with its cam-
bium-ring and central medulla. The disposition of the tissues
is readily seen in a young tuber (Fig. 143).
In a fully developed tuber the epidermis is replaced by peri-
derm, the outer layer of which consists of cork-cells ; the latter
afford protection against excessive loss of water from the interior
of the tuber. Beneath the
* skin ' or periderm is the
cortex, and in its outer cells
the cell sap is frequently
coloured, giving a charac-
teristic tint to the different
varieties of potatoes. The
Cambium in its growth pro- FlG> US- -Longitudinal section of a young
idiiiuiuiii in ua giuwiu piu potato tuber. c cortex ; v vascular bundle ; \m
duces much wood, and it is r" ll " a ; J . sca . 1 ? l f f in the axil of which is a
7 bud ; t terminal bud.
this tissue which forms the
main bulk of the tuber; instead of the wood, however, con-
sisting of lignined tissue it is almost entirely made up of
parenchymatous thin-walled cells, with only a few isolated
groups of lignified elements, and cannot therefore be readily
distinguished from the medulla and cortex.
The chief reserve-food stored in the tuber is starch, the
largest amount being found in the innermost parts of the cortex,
the degenerate wood-tissue, and part of the medulla. In thin
slices of the potato the bast, cambium and centre of the medulla
appear semi-translucent, and contain little or no starch.
GERMINATION OF THE TUBER. Ripe potatoes cannot be
468 SOLANACE^B
made to germinate before a certain time has elapsed. Some
varieties need a rest of two months only, while others ripened
in autumn do not show signs of growth before January or
February, or even later.
The minimum temperature for germination is about 8* or
10* C, so that tubers planted very early make little or no
growth.
The cause of the resting-period and the chemical changes
which go on during that time are not clear. Respiration which
is carried on at the expense of the starch can be recognised;
at first it is slow, but increases rapidly towards the end of the
resting-period.
When germination commences, the enzyme diastase is formed,
whereby the starch is changed into sugar: the latter is trans-
ferred to the growing buds, where it is utilised in the formation
of new cells. The first development of the shoots is carried on
at the expense of the stores of reserve-food within the tuber.
Rarely do two buds on the same tuber develop equally
strongly, the most vigorous being the terminal one, or the
central bud in the * eyes ' near the apex of the tuber. The
buds at the base of the tuber are weakest, and often remain
dormant altogether. When tubers are cut for 'sets' so that
each piece contains one ' eye,' those pieces from the ' rose ' end
always produce the most vigorous plants and the best yield.
If the main shoot produced from the central bud ot an ' eye '
is broken off or otherwise destroyed, the lateral buds in the
1 eye ' grow out, but their shoots are never so strong or vigorous
as the lost one.
The shoots produced from the growing buds of potatoes
exposed to the light during germination have short internodes
and scaly leaves, in the axils of which three lateral buds are
usually visible. After planting the tuber, the tip of the main
axis of each shoot grows upwards into the open air, where the
unfolding leaves carry on 'assimilation.' The food manufac-
POTATO
469
tured by the leaves passes down the stem, and from the middle
bud in each leaf-axil below ground a thin rhizome develops,
which, after reaching a variable length, generally forms a new
tuber at its end (Fig. 144). When the old dead tuber has been
exhausted of its store of food, it still contains water obtained
formed a tuber ; r roots (adventitious).
from the surrounding soil, and acts as a reservoir for the growing
plant in the dry part of the season.
It must be observed that rhizomes only produce tubers when
they are kept in the dark, hence the value of ' earthing up,'
and the necessity of doing it at intervals so that newly-formed
rhizomes resembling p in the above Fig. may be properly ex-
32
470
SOLANACE^E
eluded from the light. Rhizomes exposed to light become
ordinary green-leaved shoots.
Before planting tubers it is important to germinate them, if
possible, in the light, in order to obtain from each awakening
' eye ' a short, thick piece of stem with many nodes upon it, as
it is from the axils of the leaves at the nodes that the rhizomes
are produced which bear tubers. This practice influences the
yield to a considerable extent, for if the tubers are allowed to
start growth in the dark, either indoors or below ground, the
shoots from the ' eyes ' have longer internodes and fewer
points for the production of tuber-bearing rhizomes under-
ground ; moreover, the leafy shoots sent above ground are
weak when the latter method is adopted.
LEAF. The leaves are compound, interruptedly pinnate,
opposite pairs of small leaflets alternating with pairs of larger
size.
FLOWER (Fig. 145). The flowers are in cymes: calyx in-
ferior, gamosepalous, five-partite ;
corolla hypogynous, gamopetal-
ous, five-lobed, rotate, violet,
lavender or white. Andrcecium
epipetalous, five stamens, with
yellow anthers dehiscing by pores
at the tip. Gynsecium superior,
syncarpous, 2 carpels, ovary
bilocular.
FIG. i 4 5.--Section of potato flower, c FRUIT. The potato " apple "
calyx ; / corolla ; s stamen ; o ovary ; a . .
style ; t stigma of the gynaecium. or fruit is a berry with many
seeds attached to a thick axile placenta (/, Fig. 146.) Many
varieties of the potato rarely produce flowers when cultivated
in the ordinary way ; even those which do so are often unable
to ripen fruit and seeds. This is especially the case with varieties
which yield large crops of tubers; the latter attract the food
manufactured by the leaves, and little or none remains for the
THE LATE OR MAIN-CROP VARIETIES 471
development of the flowers and fruit. If flowers are needed
for hybridising purposes, plucking off the early-formed tubers
often produces the desired result.
VARIETIES. Considerable attention has been
paid to the improvement of the potato, and many
varieties are in existence differing in yield, ripening
period, shape, quality of tuber, and in many other
points. They may be classified in several ways, FIG. 146. Trans-
. it i j j . ^i verse section of
but are usually placed in groups according to their ovary of potato
. r . i-i i flower, a Wall of
time of ripening, their shape, or colour. ovary ; /placenta;
The early varieties are consumed in an unripe " ovules>
condition, and are adapted for forcing for early markets. To
this class belong Ashleaf, Epicure, Duke of York, Snowdrop, Early
Regent, and others.
The mid-season or second earlies are dug green for the summer
market, and may be left to mature with the later varieties. Sir
John Llewellyn, British Queen, Arran Comrade, Majestic, and
Stirling Castle belong to this class.
The late or main-crop varieties ripen in autumn, and often
grow until cut down by frost. Up-to-Date, Golden Wonder,
Kerr's Pink, King Edward VII, Ben Cruachan, may be mentioned
as typical of this section.
It is of little use to attempt to raise new varieties by selec-
tion of tubers only, as these are merely divisions of the parent
and cannot be expected to give rise to new offspring unless the
tubers chosen happen to be true bud-variations or 'sports.'
The latter are, however, of rare occurrence in the potato plant.
Marked variations are obtained in seedling plants, and it is from
these that selection is made in order to obtain new and im-
proved varieties.
The chief points of a good variety are the following :
(a) Strong disease-resisting power.
(b) Good cooking quality ; when steamed or boiled, the
tuber should break easily into a glistening floury condi-
472 SOLANACE^E
tion without any appearance of clamminess or wetness,
and should preserve a white colour even when cold.
(e) The yield per acre should be high.
(d) High starch-content is needed where the tubers are used
for the manufacture of starch or in the distillery.
(e) Shallow 'eyes/ and few of them, are looked for in the
best quality, as those with deep depressions hold dirt,
and necessitate considerable waste of substance when
peeling is practised before cooking.
(/) Good keeping quality.
(g) Trueness to type of tuber should be aimed at. Whatever
form the tuber takes whether round, kidney, or oval
the crop should be as uniform as possible in this
respect, and tendency to super-tuberation should be
avoided.
CLIMATE AND SOIL. The potato succeeds best in a warm
and comparatively dry climate, and is unable to stand frost,
exposure to a temperature of freezing point for a single night
being sufficient to destroy the stems and leaves of a young crop.
The soils best suited to its growth are deep, sandy loams,
lying upon porous subsoils; stiff clays and undrained peaty
soils, with excessive amount of moisture present, are almost
valueless for potato culture, unless well drained and cultivated,
and even then the quality of the tubers produced upon such soils
is unsatisfactory, although the yield is sometimes high.
SOWING. New varieties are raised from true seeds, the
resulting tubers being propagated for three or four years before
a decision can be arrived at in regard to their usefulness.
The main crops of the farm and garden are raised by planting
tubers ('sets'). Although large c sets' almost invariably give
the greatest yield of crop, for economical reasons tubers about
the size of a hen's egg, and weighing about 3 or 3^ oz., are
usually employed with good results. Small tubers produce weak
plants. The best results are generally obtained by planting whole
THE LATE OR MAIN-CROP VARIETIES 473
tubers ; but tubers may be cut into small pieces, each of which
may be planted provided that it bears one or more ' eyes/ from
which stems may arise.
From 12 to 18 cwt. of ' sets ' are needed to plant an acre.
Early varieties are planted in February and March, later ones
in April, in drills from 24 to 27 inches apart, the tubers being
placed about 15 inches asunder in the rows.
As far as possible the drills should run north and south, on
somewhat stiff soils inclined to dampness ; on drier soils east
to west.
YIELD. The average yield per acre is 7 or 8 tons.
COMPOSITION. The most important ingredient in the tuber
is starch, the amount of which varies from 10 to 26 per cent. ;
the best varieties usually contain about 18 to 22 per cent.
Sugar is absent from well-ripened tubers, and there is only a
trace of fat in them.
The nitrogenous substances average a little over 2 per cent.,
of which about 1-2 are albuminoids, present in the protoplasm,
in solution in the cell-sap, and also in the form of solid ' proteid-
crystals.' The latter occur chiefly in the cells of the cortex.
The water-content averages about 75 per cent.
A poisonous substance solanin is present in nearly all parts of
the plant, the young etiolated shoots of the tuber and the berries
containing most.
Ex. 238. Sow true seeds of potato plant in boxes or pots of earth, and ex-
amine at different stages of growth. Note the form of the cotyledons, the
extent and position of the root, and the origin of branches which bear tubers.
Ex. 239. Examine the arrangement of the ' eyes ' on a large, long,
coarse tuber, and note the relative number at the * heel ' and ' rose '
end respectively.
Cut longitudinal and transverse sections of the tuber, so as to pass through
one of its ' eyes, 1 and note the cortex, vascular part, and irregular outline of
the medulla.
Ex. 240. Examine several sprouted tubers which have been allowed to ger-
minate in the dark on a stable or cellar floor without touching each other.
474 SOLANACE^:
Note which * eyes ' have produced the strongest shoots, and the number of
shoots from each ' eye. '
Ex. 241. Carefully dig up a complete potato plant in June including the
old tuber. Examine the roots and rhizomes bearing the young tubers, and
note their position upon the plant. If very small tubers are present, look
with a lens for the scale leaves near their ' eyes. '
Ex. 242. Scrape away the earth from a young potato plant, and cut off all
the tubers which are beginning to form, taking care not to injure the roots.
Cover up the latter, and repeat the process at a later date. Watch the future
development, and note the formation and structure of the tubers in the axils
of the foliage-leaves.
Ex. 243. Uncover an elongated underground rhizome ot a potato plant
which has just begun to form a small tuber at its tip, and allow it to grow
above ground or on the surface of the soil where light can get at it. Observe
the changes in its appearance from day to day for a fortnight.
Ex. 244. Examine and make sections of the flower and fruit of a potato
plant, and compare them with those of the tomato and woody nightshade.
3. Belonging to the genus Solatium are two wild indigenous
plants, viz., Bitter-Sweet and Black Nightshade, both of which
are poisonous and sometimes erroneously called Deadly Night-
shade.
4. Bitter-Sweet (Solatium Dulcamara L.) is a shrubby peren-
nial common in woods and hedges. The upper leaves are
hastate, the lower ones cordate-ovate. The purple flowers re-
semble those of the potato but are smaller; the fruit is a red,
ovoid berry.
5. Black Nightshade (S. nigrum L.), is a smaller plant, herba-
ceous and annual, with ovate leaves; most frequent in waste
places. Its flowers are white, and the fruit a round, black berry.
Other plants occasionally met with belonging to different
genera of the Solanaceae are Deadly Nightshade and Henbane.
6. Deadly Nightshade (Atropa Belladonna L.) is an herbaceous
perennial, about three feet high, met with about ruins and chalky
waste places, but of comparatively rare occurrence. It possesses
large broad, ovate leaves, and purple, drooping, bell-shaped
flowers. The berries are a deep violet colour, and of sweetish
taste. The whole plant contains hyoscyamine and atropine,
HENBANE 475
both of which are extremely poisonous alkaloids. The con-
sumption of a few berries has led to fatal results.
7. Henbane (Hyoscyamus niger L.). A hairy biennial, about
two feet high, possessing a strong fetid odour, and growing on
waste ground. The broad leaves are sessile and clasping, with
pinnatifid margins ; the flowers of greenish-yellow colour, veined
with purple. The fruit is a two-celled capsule. The leaves and
flowering shoots contain the poisonous alkaloid hyoscyamine,
nearly related to atropine.
The tomato and tobacco plants also belong to this Order :
also the poisonous Thorn- Apple (Datura Stramonium L.) which
sometimes occurs in this country as a casual weed of cultivated
land.
CHAPTER XXXIV.
COMPOSITE.
i. THE Composite is the most extensive Order, and comprises
from 10,000 to 12,000 species, or roughly about one-tenth of all
known seed -bearing plants.
A number of species, such as Arnica montana L., chamomile
and wormwood, are of medicinal value ; others, of which the
artichoke and lettuce may be taken as examples, are useful food
plants of the garden.
Plants belonging to the genera Zinnia, Chrysanthemum,
Dahlia, Aster, Gaillardia, Helianthus, and others are largely
grown as ornamental plants.
Not a single species, however, is grown as an ordinary farm
crop in this country, though not a few, such as dandelion, thistle,
groundsel, coltsfoot, mayweed, and ox-eye daisy are objectionable
weeds (see pp. 602, 615).
2. General characters of the Order. The most characteristic
feature of the Order is the structure of the inflorescence : the
latter is a capitulum, and consists of a number of small flowers
collected into a compact head resembling a single large flower.
A common form of capitulum is seen in the ox-eye daisy
(Fig. 147), the parts of which, with the dandelion described below,
may be taken as typical of the commonest forms in the Com-
positae. On its underside is a series of narrow scaly bracts
termed phyllaries, arranged in whorls ; the whole series of
phyllaries is spoken of as the involucre of the capitulum.
In the centre of the capitulum are a number of small yellow
flowers the so-called disk florets each of which has the
470
GENERAL CHARACTERS OF THE ORDER 477
form shown at 2, Fig. 147. Each floret or small flower is
regular and epigynous ; the corolla gamopetalous and five-lobed ;
no calyx exists, or is only present in the form of a minute ring
round the upper part of the ovary. The androecium consists of
five stamens with filaments attached to the inside of the corolla
(epipetalous) ; the anthers of the stamens are united together,
and form a tube through which the style passes. (Stamens with
united anthers and free filaments are described as syngenesious.}
The ovary is inferior and syncarpous, consisting of two
united carpels; within it is a single erect anatropous ovule.
The straight style has a divided tip.
FIG. 147 i. Capitulum of Ox-eye Daisy (Chrysanthe-
mum Leucanthetnunt L ). r The ' ray' ; d the ' dibk."
2. ' Disk' floret (magnified), o The cvaivl c tubular
corolla ; a, anthers ; j stigma. 3. * Ray ' floret (magni-
fied), o Ovary ; s stigma ; c ligulate corolla ,/ fruit.
The fruit (/, Fig. 147) is one-seeded and indehiscent with a
series of longitudinal ribs on its outer surface : it is a kind of
nut or achene to which the special name cypsela is given.
The seed is without endosperm.
Besides the disk florets and surrounding them, there is a
single ring of white flowers (f) resembling narrow strap-like
petals. They form the ' ray ' of the capitulum, and are termed
ray florets. Each of the latter is a small unisexual (female)
flower, and possesses a white corolla, the lower part of which is
tubular, while the upper part is drawn out into a long narrow
478
COMPOSITE
structure, the tip of which is notched (3, Fig. 147). A corolla
of this form is described as ligulate. The rest of the parts are
similar to those of the disk florets.
Both the ray florets and the disk florets are sessile upon a
short, thick button-shaped axis which is designated the receptacle
of the capitulum, an unfortunate term likely to be confused with
the receptacle of a flower, with which however it has nothing
to do.
A large number of genera, the species of which have capitula
composed of tubular florets only, or of tubular florets and an
outer whorl of ligulate florets, are united to form a division of
the Composite known as the TUBULIFLOILE. Plants belonging
to this series have watery juice in their stems and leaves.
Another group of genera, termed the LIGULIFLOR^S, is formed
of those species whose capitula bear only ligulate flowers. Plants
belonging to the Liguliflorae,
of which the dandelion and
sow-thistle are examples,
have milky juice (latex] in
their stem and leaves.
A single flower from the
capitulum of the dandelion
is seen in Fig. 148. It is
bisexual with a ligulate
corolla formed of five petals
shown by the five notches
1 3.
FIG. 148. i. Single Floret of Dandelion (Tar-
at its tip. The calyx is
composed of silky hairs
which encircle the upper
part of the ovary. This ring
of hairs grows most rapidly
after fertilisation of the
flowers when the fruit is ripening: it is termed \hepappus, and
acts as a parachute for the distribution of the fruit by the wind.
axacum officin.aU Web ). o Inferior ovary ;
> pappus (calyx) ; a. anthers of stamens ; /their
filaments ; style and divided stigma ; c ligu-
late corolla.
a. Fruit (cypsela) developed from i. s Stalk
of the pappus/.
3. Fruit (cypsela) of Groundsel (Senecie
vulgaris L.) with, sessile pappus.
YARROW I MILLEFOIL OR THOUSAND-LEAF 479
In the dandelion the pappus is stalked, that is, situated at
the end of the prolonged upper part or beak of the fruit
(2, Fig. 148). In groundsel (3, Fig. 148) the pappus is
sessile.
Ex. 245. (i) Examine the inflorescences of ox-eye daisy, common daisy,
sow-thistle, dandelion, groundsel, and any other common Composite. Note
the form and extent of the involucre, the presence or absence of disk and ray
florets.
(2) Cut vertical sections of the capitula and observe the form of the
receptacles, whether flat, convex, concave, or conical. Note the presence or
absence of small bristly or chaffy scales (bracteoles) on the receptacles near
each flower.
(3) Examine the fruits of the above-mentioned plants. Note the presence
or absence of a pappus ; also the smoothness or roughness of the pericarp.
Are the hairs of the pappus simple or branched ?
3. Yarrow : MillefoU or Thousand-leaf (Achillea Millefolium
L.) is a perennial plant belonging to the Compositse, common in
poor dry pastures, and possessing an extensive creeping root-
stock. The stems are from 6 to 18 inches high, and furrowed.
The leaves are 2 or 3 inches long, narrow, oblong, and much
divided, the segments being very fine. The capitula, which
are crowded together in a corymbose manner, are small, usually
not more than \ or \ inch in diameter, with white or pinkish
ray florets.
The fruits, commercially known as ' seeds, 1 are compressed, and
have no pappus. Yarrow grows very early in spring, and pos-
sesses a strong aromatic odour when bruised. Sheep are fond
of the young leaves, and generally keep the plants eaten down
in pastures. But when it has developed its strong woody stem
stock refuse it.
Yarrow is sometimes recommended for mixture with grass
seeds when sowing down land for sheep pasture, but its use
must be restricted to the narrowest limits, or it will soon dis-
figure and usurp the ground which should be allotted to better
480 COMPOSITE
plants. It should be left out of all grass mixtures where the
produce is to be mown.
Ex. 246. Dig up and examine a complete plant of yarrow in flower. Note
the character of the rootstock, its tough stem and much divided leaves, and
its corymbose collection of small capitula.
Carefully examine a single capitulum, noting the number and form of the
ray and disk florets respectively.
Examine the fruits of yarrow.
CHAPTER XXXV.
GRAMINEJE. TRUE GRASSES.
i. General characters of the Order. Herbs. Roots fibrous,
chiefly adventitious. Stems cylindrical, hollow, with solid nodes.
Leaves alternate with split leaf-sheath and ligule.
Inflorescence a spikelet, bearing chaffy bracts or glumes, which
hide the flowers. Flower small, bisexual, hypogynous. Perianth
missing, or consisting of two scales (lodicules). Androecium of
three stamens with versatile anthers. Gynaecium a single carpel,
with two styles, having feathery or brush-like stigmas ; ovary
with one seed. Fruit a caryopsis.
a. This is one of the most valuable and extensive Orders
of plants, and comprises between 3000 and 4000 species. To
it belong the cereals which supply the chief part of the food of
the human race, and also the meadow and pasture grasses so
important as food for the stock of the farm.
The general character of the roots, stems, leaves, and flowers
of grasses are here dealt with, while in the subsequent chapters
the cereals and those grasses of which it is essential that the
agriculturist should possess a good knowledge are treated in
greater detail.
ROOT. The roots which emerge from the seeds of grasses on
germination are few in number and short-lived, but an extensive
system of adventitious, thin, fibrous roots develops later from all
the underground nodes of the stems.
STEM. The stems, which are termed culm^ are cylindrical
and usually hollow when full-grown, except at the nodes, where
481
482 GRAMINE>. TRUE GRASSES
they are solid : maize is exceptional in having stems solid
throughout.
Branches arise only in the axils of the lowermost leaves.
1 Tillering ' is the term employed to designate this form of branch-
ing in grasses, and its nature is discussed on pages 490-494.
Generally the buds break through the base of the enclosing
leaf-sheaths ; the branches produced are designated extravaginal
branches and grow more or less horizontally for a time, often
underground, forming longer or shorter rhizomes, from which
leaves and flowering stems are sent up. Grasses behaving in
this manner soon cover considerable areas of the ground with a
close turf. Couch-grass, smoothed-stalked meadow-grass, and
fiorin are good examples.
Less frequently the branches are intravaginal, that is, they
grow up between the leaf-sheath and the stem, emerging near
the ligule, but ultimately, tearing the subtending leaf, as in x,
Fig. 153. Branching of this character leads to the formation of
compact tufts, and grasses exhibiting this manner of growth are
unable to cover the ground except in isolated patches. The
cereals (see pp. 490-494), annual broine-grasses, meadow and
sheep fescues, rye-grasses, and cocksfoot are examples.
The perennial rhizomes of grasses are usually sympodia
(2, Fig. 22).
LEAF. The leaf of a grass consists of two parts, the blade
and the sheath. The Uaf-shtath surrounds the stem like a tube
split down one side, its free edges overlapping in some instances
(&Fig. 149). In cocksfoot, dodder-grass, and some of the meadow-
grasses it is not split but forms a completely closed tube. It acts
as a support for the stems while they are young and soft, and
protects the tender growing points within from the injurious
effects of frost and heat. Most grasses appear swollen at the
nodes (d, Fig. 149) ; this is not usually due to thickening of the
stem, but to the presence of a mass of soft tissue at the base
of the leaf-sheath.
484
GRAMINE^E. TRUE GRASSES
The leaf-blade is generally long, narrow, and flat, but in
grasses growing in dry places it is often folded and appears
almost cylindrical (Fig. 183).
The first leaf of the embryo and those upon the underground
rhizomes are almost always modified structures representing leaf-
sheaths the blades of which remain undeveloped or rudimentary.
It is important to notice the arrangement of the leaves in the
bud as it often affords a ready means of
distinguishing nearly -allied species of
grasses. Most frequently the leaves are
rolled up from one side in a spiral form,
and the young shoot appears round (Fig.
191), but in several grasses they are
simply folded down the middle, the shoot
then appearing flattened (Fig. 188).
At the point where the
blade 'joins the sheath the
inside of the latter often
protrudes as a tongue-like
membranous structure (/
Fig. 149), termed the ligule.
Fig. 150. i. Spikelet from grass of Fig. 149. rr> , . . , .
t. The same slightly opened to show separate 1 lie latter VariCS HlUCh 111
length in different species.
Near the ligule the sides of
the leaf sometimes terminate
in claw-like projections which partially or entirely encircle the
stem as in Figs. 154 and 189.
INFLORESCENCE. In the figure of annual meadow-grass (Fig.
149), the branched upper part popularly termed the * flower '
is a complex inflorescence bearing flowers which are very small
and completely hidden from view. The parts c are termed
spikelcts, and it is within these that the flowers are enclosed.
A single spikelet is illustrated in Fig. 150. On examination
it is seen to consist of an axis r y the rachilla^ upon which is
glumes and florets, a Empty glume ; /flowering
glume of second floret; rrachilla or axis of spikelet.
3. Single floret of 2. f Flowering glume ;/ palea;
o ovary of gynaecium ; r piece of rachilla.
4. The flower. / Lodicules; o ovary ; s stigma ;
a stamen.
GENERAL CHARACTERS OF THE ORDER 485
arranged a series of sessile bracts in two alternate rows. These
bracts are termed glumes, and in the axils of all except the two
lowermost ones (a a) flowers are produced which on account of
their small size are not seen. The glumes a a are termed the
empty glumes of the spikelet, the others similar to / are the
flowering glumes. Attached to the very minute stalk which
each flower possesses is another bract, named the/a/<? or palea
seen at p. It lies opposite to the flowering glume, and be-
tween it and the latter the flower is enclosed more or less
completely.
The empty glumes are usually two in number, but there is
only one in rye-grass, and the spikelet of sweet vernal-grass
possesses four. Sometimes they are small and narrow as in rye,
or they may be large and completely enfold the rest of the
spikelet as in oats.
The flowering glumes often differ from the empty ones in
having 'beards' or bristle-shaped structures termed awns. In
barley and ' bearded ' wheats the awns are of great length, while
in some instances they are merely short points at the tip of the
glume.
Awns are said to be terminal, dorsal, or basal according to
whether they arise from the tip, middle of the back, or the base
of the glume.
The number of flowers in each spikelet varies considerably: in
some species, as timothy grass and florin, only one is present, in
Yorkshire fog two, while in meadow-grasses, fescues, and rye-
grasses there are several.
All our grasses resemble each other in having their flowers in
spikelets, the latter, however, do not constitute the whole in-
florescence but are only parts of it In wheat, rye-grass, and
barley the spikelets are sessile upon opposite sides of a straight
unbranched main axis, the rachis, the total inflorescence being
termed a spike ; in reality it is a spike of spikelets.
In the majority of grasses the rachis is much-branched and
33
486 GRAMINE^E. TRUE GRASSES
the spikelets are borne at the ends of the branches as in Fig. 149.
Such an inflorescence is termed a panicle.
When the branches of the panicle are long and the spikelets
consequently separated from each other, the panicle is described
as spreading open, or diffuse (Figs. 174, 181, &c.).
When the branches of the panicle are very short, so that the
spikelets lie close to the main axis as in foxtail and timothy grass
(Figs. 172 and 173), a false spike or spike-like panicle is formed.
THE FLOWER. As pointed out previously the glumes are bracts
of the inflorescence and do not, of course, constitute a part of
the flower. The latter (4, Fig. 1 50) consists of an androeciurn of
three hypogynous stamens and a gynaecium of one carpel. At
the base of the ovary on the side opposite to the pale, that is,
on the side next to the flowering glume, there are two small
transparent scales, the lodicules^ /; they are usually considered
rudiments of the perianth, but may possibly represent a second
palea.
The filaments of the stamens are long and slender and
attached to near the middle of the anthers ; the latter are readily
moved by the slightest breeze.
In sweet vernal-grass two stamens only are present.
The gynaecium consists of a single carpel with an ovary most
frequently surmounted by two styles with brush-like stigmas (j).
The grasses are cross-fertilised, though self-fertilisation is also
frequent At the time of flowering the base of the lodicules
generally swell up and force the pale and flowering glume
apart; the filaments of the stamens grow rapidly about the
same time and push the anther out at the sides of the
glumes ; the pollen is then distributed by the wind and caught
by the feathery stigmas.
In a short time (often not more than an hour or two) the
lodicules lose their turgidity and shrivel, and the pale and
flowering glume close up again shutting the ovary and stigmas
from view.
GENERAL CHARACTERS OF THE ORDER 487
THE FRUIT AND SEED. The fruit of grasses is in most cases
a caryopsis or a one-seeded form of nut, the seed of which has
grown completely into union with its surrounding thin pericarp.
The wheat grain discussed on p. 22 may be taken as typical of
a caryopsis and its enclosed seed.
In young flowers the ovaries of the grasses are quite free from
the glumes and may remain so even when the fruit is ripe as in
the case of wheat, rye and oats; sometimes, however, during
growth after fertilisation the caryopsis grows up to between the
glumes and becomes united with the latter as in the case of
ordinary barley.
In oats and many grasses the glumes so closely invest the
caryopsis that the latter does not fall out from the glumes when
the ripe panicles are shaken or thrashed ; nevertheless, in these
cases the caryopsis is free and easily separable from the glumes,
which is not the case in barley and many other grasses.
The seed contains a large proportion of starchy endosperm,
at the side of which the embryo is placed. In some grass seeds,
and particularly those of certain varieties of cereal grains, such as
Hard wheats, the endosperm is flinty^ or hard and semi-trans-
parent, while in others the endosperm, which is described as
mealy> is opaque and chalky when cut across.
The different appearance of flinty and mealy endosperm is
due to the fact that in the first the starch grains within the cells
are embedded in a dense matrix of proteid material, while in
the mealy endosperm the cells are not completely filled with
reserve materials, but very minute air spaces exist between the
starch-grains within the cells.
The embryo (Figs. 7 and 151) possesses one cotyledon (the
scutellum), a short plumule, and in most cases a single primary
root covered by the coleorhiza. In the cereals and some other
grasses secondary roots appear upon the very short hypocotyl of
the embryo while the latter is still within 'the caryopsis and they
make their exit at the same time as the primary root, when
488 GRAMINE^E. TRUE GRASSES
germination commences; in most grasses, however, secondary
roots first appear some time after the single primary root has
grown out from the caryopsis.
Ex. 247. Examine the roots of any grass. Observe as far as possible
their origin, and note if they branch extensively.
Ex. 248. Cut transverse and longitudinal sections of any well-developed
grass stem at and between the nodes. Note if hollow or solid all through.
Examine the leaves of barley and oats and many common grasses. Note
the split leaf-sheath, the flat or rolled blade, and the character of the ligule
if present.
Ex. 249. Make an examination of the inflorescences of a number of common
grasses in order to understand the various parts, viz., the rachis, and the
spikelet with its rachilla and bracts. Which are the empty glumes, flowering
glumes, and palea in each spikelet ?
Ex. 250. Dissect out the flowers from any common grasses, noting the form
and position of the stigma, the number of stamens, and the position, number
and form of the lodicules in each.
Ex. 251. Watch the unfolding of the total inflorescences of Yorkshire Fog,
Tall Oat-Grass, and other grasses with panicles. What positions do the
branches take before and after flowering ?
Ex. 252. Cut transverse sections of several grains of barley, oats, wheat,
rye and maize. Note the ' mealiness ' or ' flintiness ' of the endosperm in
each.
CHAPTER XXXVI,
GRAMINE43 (continued). CEREALS.
IN Europe perhaps the most familiar crops of the farm are wheat,
barley, rye, and oats.
These crops, designated Cereals, are grown mainly for their
fruits or grains which form the most important food of mankind
and are also of great value as food for the stock of the farm.
Besides being utilised as bread-corn large quantities of the
cereal grains are employed in the manufacture of starch, beer,
whisky, gin, and other spirits.
Moreover, the cereals are frequently grown for green fodder and
the straw in a ripe state is fed to stock, made use of as litter, or
employed for thatching, and many similarly useful purposes.
The common cereals of the tropics are rice, maize, millet, and
sorghum or dourra, but these, with the exception of maize, which
is occasionally employed in a green state as horse and cattie
fodder or made into silage, have no practical interest for the
farmer of this country.
The cereals are grasses and therefore possess general char-
acters described in the last chapter \ they are, however, of such
importance that further treatment of their peculiarities is needed.
FRUIT AND GERMINATION OF SEED. (a) An account of the
fruit and the germination of the embryo of wheat has previously
been given (chap, ii.); the grain of rye is similar to this in
almost all respects, but the roots of its embryo are generally four
in number instead of three as in wheat.
(b) In barley the caryopsis or fruit is firmly united with the
enclosing flowering glume and pale, and the plumule of the
489
490
GRAMINE^E. CEREALS
embryo does not make its exit where the coleorhiza and roots
emerge but grows on beneath the glume, and ultimately appears
at the opposite end of the grain sometime after the roots have
come forth (Fig. 151).
The number of roots vis-
ible on the embryo within
the barley grain is generally
five or six.
(c) In the oat the caryopsis
is free from the glumes, but
the latter more or less tightly
surround it and on germina-
tion the plumule of the em-
bryo behaves as in barley, and
emerges from the grain at the
end opposite to that at which
the roots appear ; the number
of roots of the embryo is
three.
ROOTS. In the cereals, as
in all grasses, the roots of
the embryo within the seed
Fio^s^Barleygrainshowingembryo^dits
Ut
Commences I
germination
these may be
J
termed 'seminal* roots. They
'
development during germination. .
1. Longitudinal section of gram showing
embryo at rest.
2. J he same after germination has begun ; the
roots have made their exit from the gram, but the are of importance in the early
Slumule c is still within it enclosed by the . '
owering glume. life of the young plant, but
3. Later stage of the germinated grain showing ' .
the plumule c outside the grain. subsequently die off and their
e Endosperm; a. coleorhiza; b root; c plumule; .
^scuteiium. work is undertaken by the
so-called ' coronal* roots which arise from the lower nodes of the
stems as explained below (see Figs. 152 to 154);
* TILLERING/ A^ Fig. 152 gives the appearance of a young
barley plant after a single green leaf has appeared above ground.
At this stage it possesses a small bunch of roots which have come
GRAMINE^E. CEREALS
491
from those which were easily seen in the embryo within the
seed.
Soon afterwards more leaves show themselves, as at B, Fig.
152, and often about the same time the terminal bud, which was
A B C
FIG. 152. A, Young barley plant, showing 'seminal roots, c First sheathing leaf;
/ blade of first green leaf.
B, Young barley plant, a later stage of A. a 'Seminal* roots; n first node of
stem.
C, Longitudinal section of B at *. c Sheathing leaf ; Astern; a terminal bud; b lateral
bud (first k tiller 4 ) ; e adventitious root forming.
originally within the grain, is carried up to near the surface
of the ground by the growth of the first internode, the second
and succeeding internodes remaining undeveloped for some
time. When the primary bud has reached this position rapid
formation of lateral buds takes place in the axils of its leaves.
492
GRAMINE^E. CEREALS
A longitudinal section of a portion of a plant in this early stage
is seen at C, Fig. 152, where a is the terminal bud, and b a
lateral bud just forming. In Fig. 153 a similar plant is shown in
a further stage of development ; the leaves of bud b have now
come above ground.
A shoot may arise in this manner in the axil of each of the
lower leaves on the primary stem, the internodes of the latter
FIG. 153. I. Young barley plant, a later stage of B y Fig. 152. The leaves from bud If
in latter figure haxe now grown out and burst the enclosing leaf-sheath.
II. Longitudinal section of I. at first node , showing the short stem within terminated
by a minute ear. Besides the bud b a rudimentary one is seen in the axil of the lower leaf
of the main stem, e Adventitious root ; n first node.
remaining very short all the time (//., Fig. 153). The secondary
stems may also develop in a similar fashion. It is thus seen
that from a single grain the production of a large number of
shoots is possible, and these breaking their way out from the
enclosing leaf-sheaths appear finally as a tuft of stems, each of
which may subsequently develop an ear of corn.
This formation of many shoots which spring from near the
GRAMINE^E. CEREALS 493
surface of the soil is termed * tillering] and is a common mode of
branching met with in all the cereals, and in grasses generally.
No matter at what depth the seed is placed branching only
takes place at the nodes near the surface of the ground. If
placed deeply the first internode or two (d, C, Fig. 152, and a,
Fig, 154) elongate considerably, and are noticed as a tough,
wiry piece of stem when the plants are pulled up ; in shallow
sowing the internodes are short and scarcely visible.
The number of ear-bearing shoots produced from a single
grain may, under some circumstances, be 100 or more; usually
it is not more than five or six. Varieties of cereals grown largely
for straw should tiller considerably ; for production of grain of
good quality two or three stems from each is sufficient. The
ears of much-tillered plants ripen unevenly as the stems are neces-
sarily not all of the same age, and those produced last are
smaller and weaker than the primary stem and its first two or
three branches.
The amount of * tillering ' depends upon both internal and ex-
ternal causes. Some species of grass * tiller' more than others
wheat and barley, for example, more than oats ; varieties of the
same cereal also differ considerably in this respect.
Plants exposed to plenty of light * tiller ' more extensively than
those grown in shade. Thin-sowing promotes it by allowing
more light to reach each plant. Moreover, in thin-sown crops
more food-constituents are at disposal in the ground for each
plant than when crowded together, and the plants ' tiller ' more
in consequence.
On poor soils fewer stems arise from a single plant than on
good soils, and early sowing gives more time for the formation
and development of shoots, winter-sown wheat * tillering ' more
than that drilled in spring.
1 SHOOTING ' OF THE CORN. The branches for some time after
they are produced in the * tillering ' process remain with unde-
veloped internodes ; and it is only the blades of the leaves upon
494
GRAMINE^E. CEREALS
each shoot that are seen above ground in spring, the actual stems
being extremely short and quite close to the
ground. A longitudinal section of the lower
portion of the young plant at //., Fig. 153
shows the disposition of its parts.
It is seen that even in this stage the main
stem is surmounted by a visible ear, and it
will be readily understood that grazing the
crop by running sheep over it, or mowing off
the leaves in spring, does not injure either
the stem or the ear, as the latter are placed
so low down and are protected by the en-
veloping leaf-sheaths.
In the middle of June or thereabout the
rapid extension of the internodes takes place
and the corn is then said to
shoot. The ear and lowest
internode in the bud begin
to grow first ; the rest of the
stem then develops in or-
derly succession from below
upwards and forces the ear
out of the uppermost leaf-
sheath.
Germination, * tillering/ and
c shooting ' of spring-sown
crops proceed more or less
continuously without any dis-
tinct cessation of growth, but
autumn -sown cereals grow
little in winter.
1 LODGING ' OR * LAYING '
OF CROP. It is noticed that
after ' shooting' into ear
FIG. 154. I. Barley plant 6 inches high, just
commencing to ' shoot, a Rhizomatous stem ;
j, primary stem; a and 3, 'tillers' lateral
branches ; f seminal roots ; e adventitious roots.
II. Same barley plant with leaves removed to
show primary stem and five oranches 'tillers'
springing from its lower nodes ; the primary stem
has begun to 'shoot,' i e. its nodes are lengthen-
ing rapidly ; a small ear is visible at Its tip.
GRAMINE^E. CEREALS 495
corn crops very frequently become 'laid' or 'lodged.' The
straw is weak and it is found that the second and third inter-
nodes near the ground are longer than usual and the cells
beneath the epidermis and round the vascular bundles, upon
which the stems depend for mechanical support, are longer and
have thinner walls than those of straw which is not laid.
The weakness is not caused by a deficiency in the amount of
silica in the cell walls as was formerly imagined, but is due to
an inadequate supply of light to the young plants, the lower
parts being etiolated by overcrowding.
Nitrogenous manures tend to the production of much leaf
surface in all plants, and when used in excess on corn crops the
plants shade each other and are liable to become laid in
consequence.
Heavy rain and wind increase the evil, but the weakness may
be such that the weight of the upper part of the straw is sufficient
to make it fall without the aid of wind or rain.
It might be imagined that well-tillered crops, where many
stems arise from each plant, would be specially subject to
( lodging. 1 This is, however, not usually the case ; the ' tillering '
process is dependent upon light, and the fact of its having gone
on extensively is evidence that each plant has had an adequate
exposure to light; shaded plants * tiller ' very little.
Thick-sowing or drilling in too close rows promote c lodging,*
for from the first soon after germination the plants shade
each other.
FLOWERING AND FERTILISATION. Most cereals open their
flowers in the morning from four to seven o'clock and only when
the temperature rises to about 75 F. At the time of flowering
the flowering glume and pale are forced apart by the increased
turgidity of the lodicules, and the anthers are pushed out by the
rapid growth of the filaments of the stamens. At the same time
much of the pollen is shed into the air, but in almost all cereals
some of it falls on the feathery stigmas of the same flower, and
496 GRAMINE/E. CEREALS
self-pollination results. In wheat, barley and oats self-pollina-
tion is followed by fertilisation and the production of fertile
seeds, whereas in rye self-pollinated flowers are almost always
sterile and considerable decrease of yield results to the crop
when damp, dull weather prevails for a long time and prevents
the proper opening of the flowers and distribution of the pollen.
In wheat the first flowers to open are those situated about one-
third of the way from the apex of the ear, the rest follow in
succession upwards and downwards from this point. Each
flower remains open from 8 to 30 minutes, and the whole ear
completes its flowering usually in eight or nine days,
In barley the complete period of flowering of the ear is shorter,
and when the flowers open they remain expanded a longer time
than those of wheat. Frequently, however, the flowers of barley
never open at all and self-fertilisation is the rule. In fact all the
cereals, except rye, are generally self-fertilised, although natural
crosses among wheats and among oats have been observed
occasionally. Hybrids between rye and wheat have been pro-
duced.
RIPENING. A few hours after pollination the pollen-tube
reaches the ovule, and fertilisation of the ovum is effected. The
latter then gradually becomes an embryo and in the embryo-sac
around it the formation of endosperm-tissue takes place.
Within the endosperm-tissue there is also a gradual accumula-
tion and storage of proteins and carbohydrates.
Some of the proteins are laid down in the outermost layer of
cells of the endosperm in the form of aleuron-grains, and it is
important to note that the filling of the aleuron-layer and the
parts immediately beneath it takes place before the central portions
of the endosperm are completed. In small and rapidly-ripened
grains of cereals the percentage of proteins in comparison with
the carbohydrate starch is higher than in slowly-matured plump
grains in which longer time has been allowed for the accumula-
tion of starch*
GRAMINE^E. CEREALS 497
In barley for malting purposes, where the proportion of nitro-
genous compounds should be as low as possible, it is essential
that the crop should have time to accumulate carbohydrates in
the grain in large amount or its value for malting is much reduced.
While the ear and grains are ripening, changes are going on
in the roots, stem and leaves. There is a general movement
of water from below upwards and at the same time a transla-
tion of useful plastic materials (sugars, amides and proteins)
from the lower leaves and stem to the upper parts of the plant,
these materials being finally utilised in the formation of the
embryo and its store of starch and other reserve-foods in the
neighbouring endosperm-tissue within the grain.
Death also takes place, gradually from below upwards, the
roots dying off some time before the grains are ripe.
Although the ripening changes go on continuously it is useful
to notice four stages, known respectively as (i) the milk-ripe,
(2) the yellow-ripe^ (3) ripe> and (4) the dead-ripe stages.
In the milk-ripe stage the endosperm tissue contains much
water and when the grain is squeezed a white milky juice oozes
out consisting of the watery cell-sap and numbers of starch
grains. Although the lowermost leaves are dead the leaf-
sheaths and the blade of the uppermost leaf are still green ;
the glumes are also green, so that the whole crop wears a
green unripe tint.
In the yellow-ripe stage, on cutting across or breaking the
grain, the endosperm is found to be somewhat tough and kneads
like wax. The pericarp of the grain has lost its green colour and
the straw has assumed a yellow tint, except at the upper nodes
of the stem where the cells are still soft and sappy and contain
green chloroplastids.
In the ripe stage, which in hot weather occurs three or four days
after yellow ripeness, the straw is usually of lighter tint, and the
nodes which die last are now dead, shrunken, and brown. The
grain is harder and firmer.
498 GRAMINE^E. CEREALS
If left longer the crop becomes dead-ripe^ in which state the grain
is brittle when cut across or broken, and the straw loses much of
its brightness ; if left on the field the straw also is liable to
become greyish and dirty in appearance, and often so brittle that
in certain varieties of cereals the ears may drop off whole, and
much of the grain be lost in handling the crop.
For most cereals it appears to be best to cut the crop in the
yellow-ripe stage when no trace of chlorophyll can be detected
in any part of the pericarp of grains selected at random in
several parts of the field.
Ex. 253. Germinate grains of all the cereals on damp blotting-paper and
carefully note the number of roots which make their appearance from the
different kinds. Observe the way in which the plumule makes its exit from
the grain. Extract the embryos complete and note the shape of the scutellum
in each.
Does a naked caryopsis of oat or barley germinate similarly to that of
wheat ?
Ex. 254. Carefully dig up young plants of any of the cereals and note the
position and number of the ' coronal ' and ' seminal ' roots.
Ex.255. Make longitudinal sections of young ' untillered ' plants and
1 tillered ' ones in early spring or winter. Examine with a lens or microscope
and observe the number of axillary buds.
Ex. 256 Make similar sections when the stems are 6 or 8 inches high, and
note the presence and position of the young inflorescences or * ears ' within.
Ex. 257. Examine an ear of wheat, barley, and oats just after it appears
from the uppermost leaf-sheath. Note the character of the flowers. Make
examination at intervals later in order to watch the growth of the caryopsis
between the glumes. Which grains of the ear develop most rapidly ?
Ex. 258. Cut across grains at various intervals and observe the different
changes which come over the grain and its contents during ripening.
Note the order of disappearance of greenness from the stems, nodes, leaf-
sheaths, and leaf-blades. Endeavour to observe the (i) milk-ripe, (2)
yellow-ripe, (3) ripe, and (4) dead -ripe stages, and how they pass one into
the other.
CHAPTER XXXVII.
CULTIVATED AND WILD OATS (Genus A vena).
i. Characters of the Genus. The inflorescences or ' ears ' of oats
are panicles, the branches of which in some races spread out
widely, while in others the branches are more or less closely
pressed to one side of the main axis.
The spikelets contain from two to six flowers ; the empty
glumes are membranous, unequal, many-nerved, and generally
longer than the spikelet (Fig. 156). The flowering glume
terminates in two more or less distinct projecting points, and
is thick and' firm with a bent,
twisted dorsal awn ; the awn of
the flowering glume is missing
from some of the finest cultivated
oats. The empty glumes are
always pale yellow or straw colour,
but the flowering glumes may
be white, yellow, dun, brown or
black.
The caryopses are spindle-
shape, furrowed on one side, free,
hairy on the tip and sides, and firmly clasped by the flowering
glume and pale, except in the naked oat, the fruit of which
readily falls out from between the glumes when shaken or
thrashed.
The following are the chief species and varieties met with
on the farm :
2. Wild Oat (Avena fatua L.). A common weed with long
499
of Wild Oat (AvfM
500 CULTIVATED AND WILD OATS
slender stems and large open spreading panicle. The spikelets
generally contain three flowers, the flowering glumes of which
bear a strong bent awn. The rachilla and base of the flowering
glumes are covered with long reddish-brown hairs (Fig. 155).
3. Bristle-pointed Oat (Avena strigosa Schreb.). An annual
weed often confused with the previous species, from which it
differs in having one-sided panicles and fewer branches. The
flowering glumes are, moreover, more deeply divided at the apex
and the two segments prolonged into short bristles or awn-like
projections ; the rachilla and base of the flowering glume are
smooth.
This species was formerly cultivated on poor exposed land
in the northern parts of Scotland as a bread-corn, but is now
most frequently seen as a weed among the superior cereals.
It is also sometimes cultivated as green fodder for cattle.
4. Animated or Fly Oat (Avena sterilis L.). A species grown
in gardens as a curiosity. The panicle is spreading and the
' grain ' very much resembles that of the wild oat, except that
it is much larger and has longer reddish-brown hairs on the
flowering glume ; the rachilla is glabrous. When the dry, strong
twisted awn absorbs moisture it untwists and gives a creeping
motion to the grain.
5. Short Oat (Avena brevis Roth.). A species of oat with
thin grass-like stems and bulky crop of leaves, sometimes grown
for green fodder for cattle or to be made into hay.
The panicle is one-sided and the spikelets contain one or twc
flowers with awned flowering glumes. The ' oats ' are plump,
brownish and about a quarter of an inch long.
6. Common Cultivated Oat. This cereal in the northerr
countries of Europe is an important bread-corn, but in th<
warmer and drier parts the grain is chiefly used as food foi
stock, especially horses. It is also grown as an early spring
green crop.
TARTARIAN OATS 501
The various cultivated forms appear to have been derived from
the wild species, A.fatua L., A. stcrilis L., and A. barbata Brot.
Two races are recognised which are sometimes treated as
distinct species, viz. :
RACE I. Common Oat (A vena sativa L.) with open spread-
ing panicles (Fig. 157), and
RACE II. Tartarian Oats (Avena orientalis Schreb.) with
contracted one-sided panicles (Fig. 158).
The spikelets usually contain two or three flowers, the upper
one of which is liable to produce either a small grain or none at
all. The flowering glume of the lowest flower frequently bears a
straight awn ( Fig. 1 56) which when strong is
a sign of degeneration of the stock or an
evidence of the coarseness of the variety.
There is considerable diversity among
the different varieties of cultivated oats in
(i) the colour and thickness of the husk
or flowering glume ; (2) the form of the
grain ; (3) the period of ripening ; (4) the
length of the straw, and (5) the tendency
to shed the grain when ripe. ij
For meal the grain should be somewhat Flf x , 6 _ Spikclct O f common
short and plump, with a thin, clean white <^^^^^ft
husk : the varieties with long grains are /%J - /f8 three flowcrs -
best adapted for feeding stock, and the colour of the husk is of
little importance. In some districts black oats are preferred
apparently with no-sufficient reason, except that in such localities
the black varieties are the most productive and the most familiar.
The early varieties give a larger yield of grain, but less straw
than the late varieties. These oats, which are easily shed when
ripe, have thin husks as a rule and are of better quality for the
manufacture of oatmeal.
Late varieties possess longer grains, more adapted for feeding
stock, with thickish husk and a comparatively small proportion
3 Tr
502
CULTIVATED AND WILD OATS
of ' kernel.' They produce, however, a larger bulk of superior
straw, are hardier and more suited to inferior soils than the
finer early varieties. On good soils too much straw is produced
and the crop is liable to become 'laid.'
RACE I. Common Oat (Avena sativa L.).
FIG. 157. Panicle of Common Oat (Avena sativa L.).
The following are a few of the commoner varieties of this race
usually met with in this country.
(i.) Potato Oat. An early and prolific variety with a somewhat
compact ear and pale yellow straw of medium length. The grain
is white, short and plump, and of excellent quality for millers ;
its flowering glumes rarely bear awns unless the stock is
degenerating.
TARTARIAN OAT 503
It is liable to shed its seeds when too ripe, and is best suited
to good soils in a favourable climate.
Early Hamilton appears to be an improved earlier form of the
potato oat with superior straw and said to be more productive.
(ii.) Sandy Oat. A tall, stiff-strawed early oat with small grain,
the colour of which is white with a reddish tinge. It is inferior
in quality of grain, but is much less liable to shed the latter
in a gale than the potato oat. It is suited to all classes of
soils.
(iii) Abundance. A white, late variety, much grown at the
present time : the straw is tall and leaves broad with a bluish
green hue. Grain white, plump and large, with a thick husk.
It is very similar, if not the same, as Newmarket, Giant Eliza,
and Ligowo oats. Victory Oat also resembles Abundance in
some of its characters.
(iv) Golden Bain. An early oat with yellow grains in small
spreading panicles. It is a prolific sort, with stout straw.
(v.) Winter Dun or Grey Oat. This variety is sown in the
southern parts of this country in autumn, and fed off green with
sheep in spring, after which it is sometimes left for seed.
Though not unfrequently killed by severe frost it may be
considered hardy, and gives a fair yield of grain. The husk of
the grain is dark at the base, brown in the middle, and pale
brown at the tip, somewhat resembling that of a degenerate
black oat.
Several varieties of common oat having longish thin grains,
with reddish, bluish, and black husks respectively are met with ;
some of them are prolific but of poor quality, and scarcely
deserving of cultivation even as food for stock.
RACE II. Tartarian Oat (Avena oritntalis Schreb.) (Fig. 158).
The varieties belonging to this race have one-sided panicles,
as explained previously, and spikelets, whose empty glumes are
slightly longer than those of the common oat.
The grains are long, often of low bushel-weight, and wanting
504 CULTIVATED AND WILD OATS
in plumpness ; the straw is stiff and reedy, and inferior in feeding
value to that of the previous race.
Their productiveness, however, is superior to that of the
common oats, and especially is this the case upon soils in
warm climates unsuited to the growth of the latter race.
In the south of England, where as much straw and grain as
possible is the object without much regard to quality, these
varieties are very extensively cultivated.
Tartarian oats are adapted for cul-
tivation on marshy and peaty soils,
heavily dunged hop-gardens, and, in
fact, on all soils in which a considerable
amount of humus is present.
The following are two common
varieties :
(i.) White Tartarian Oat. A late
variety, with very tall stiff straw, and
grain the husk of which is dull white
with a long awn. It requires a good
soil for satisfactory growth.
(ii.) Black Tartarian Oat. One of
the most extensively cultivated black
oats, earlier and more liable to shed
its grain than the white Tartarian oat.
The straw is of medium length, the
grain black with paler tips, and plumper
than the white variety; the awns on
the flowering glumes are not so stout
FIG. i 5 8.-"panicle of Tartarian as On the latter kind.
O* (Anna orientate Schr*.). g^ kjnds Qf Tartar j an Qats are
grown for horses, sheep, and stock generally, but the black
variety sometimes yields good meal.
CLIMATE AND SOIL. Oats require a cool, moist climate ; the
north and west of the British Isles therefore grow better samples
BLACK TARTARIAN OAT 505
than the south and east. In a dry climate, unless the soil is
retentive of water, the oat develops a long thin grain, and a thick
husk, which often bears a strong awn ; the branches of the
panicles become dry and apparently hinder the translocation of
materials necessary for the formation of a plump grain.
This cereal may, however, be grown upon almost all classes of
soil
SOWING. With the exception of the winter dun oat and one
or two similar varieties, oats are sown in spring. In the south
of England they are generally drilled or broad-casted in January
or February, while in the north the crop is sown in March and
April.
When drilled 3 to 4 bushels of seed per acre are used, accord-
ing to the size of the grain, the tillering power, and the locality.
Up to 6 bushels per acre are broadcasted.
YIELD. The yield of grain per acre varies from 40 to 80
bushels or more ; the straw weighs from 25 to 40 cwts. per acre.
COMPOSITION. Oats have more * fibre ' than any of the other
cereals, reaching on an average 10 per cent, of the grain. The
soluble carbohydrates average 57 per cent. \ the fat-content is
over 5 per cent, an amount much higher than any other cereal
except maize. The albuminoids average about n per cent
Ex. 259. Examine the spikelets of any common oat. Note the number of
flowers in each, the form and extent of the empty and flowering glumes, and
the form of the naked caryopsis.
Which flowering glumes have awns?
Ex. 260. Compare the inflorescences of Tartarian and Common Oats, and
also the grains and flowering glumes of each.
Ex. 261. Examine and compare the spikelet and grain of a wild oat with
that of any of the cultivated forms.
CHAPTER XXXVIII.
CULTIVATED BARLEYS (Genus Hordeuni).
i. Characters of the Genus. The inflorescences or * ears' are
spike-like and consist of many groups of three single-flowered
spikelets (Fig. 159) arranged from top to bottom of an elongated
rachis.
Each spikelet appears practically sessile on the rachis ; but
a triplet of single-flowered spikelets really represents a primary
branch with two opposite lateral
branches each bearing one
flower. The rachilla on which
the spikelet grows laterally is
prolonged and appears as a
small bristle - like structure,
readily seen with a lens, lying
within the * furrow ' of a barley (
grain as in Fig. 163.
The groups of spikelets are
arranged alternately at notches
j r ,1 i- FIG. 150. A Piece of rachis of six-rowed
On Opposite Sides Ot the rachlS, barl( . y showing a triplet of single-flowered
so that the whole ear appears to /flowering glume! fthe ear ' * empty fi ume '
have six longitudinal rows of shfiinga^Hpie^
the central flower fertile, the two lateral
flowers (a) imperfect, r Rachis of the ear ; e
e \f flowering glume ; a imper-
The empty glumes (e, Fig.
159) are very narrow and stand
side by side in front of the flowering glume. The latter is
broad and possesses a long awn which acts as a transpiring
organ. The longest awns are usually attached to the largest
606
FOUR-ROWED BARLEY 507
and best developed grains ; when the awn is cut off or destroyed
the grain is long and thin when ripe. Usually the flowering
glume is pale yellow, but in some varieties it is black or deep
purple.
The fruit or caryopsis in the commoner varieties of culti-
vated barleys is adherent to the flowering glume and pale, and
on being thrashed does not separate from the latter.
Varieties termed naked barleys, however, exist, in which the
caryopsis is free from the glumes and falls out of the ear as
readily or more so than a grain of wheat.
2. Cultivated Barley (Hordeum sativum Pers.). The cultivated
forms of barley are all considered to belong to one species,
which has been named Hordeum sativum ; this has probably
been derived originally from a two-rowed species Hordeum
spontaneum Koch., which is met with wild in Western
Asia.
The cultivated varieties fall into the three undermentioned
races, which have sometimes been treated as distinct species :
RACE I. Six-rowed Barley (Hordeum sativum hexastichon =-
H. hexastickon L.) (A> Fig. 160). In the six-rowed barleys all the
flowers of each triplet of spikelets on both sides of therachis are
fertile and produce ripe fruits, hence the ear possesses six longi-
tudinal rows of grain : moreover, the rows are arranged at equal
distances from each other all round the rachis.
This race has short erect ears, short straw, and coarse thin
grain. It is hardy and gives a good yield, but is rarely met
with, as the very poor quality of its grain debars it from being
of any use to the farmer in this country.
RACE II. Bere: Bigg: Four-rowed Barley (Hordeum sativum
vulgar* = Hordeum vulgare L.) (J3, Fig. 160). In this race all the
flowers of each triplet are fertile and the ear is possessed of six
rows of grain as in the previous race ; the rows, however, are not
arranged regularly at equal distances round the rachis. The
central fruits of each triplet form two regular rows on opposite
^:^^|Ty';f;^v|jf^
A B W
FIG. 160. A, Six -rowed Barley (Hordtum htxatttchon. L,.).
B, Here (Hordcutn vutg*rt L ).
C. Himalayan Barley {H*rd*um tvifitrc+tutn Jacq.)
FOUR-ROWED BARLEY 509
sides of the rachis, but the lateral spikelets of each triplet which
in the six-rowed race form four straight single regular rows, in
this race form two irregular double rows, hence the whole ear
appears irregularly four-rowed, especially in its upper part.
Bere, of which there are one or two improved varieties,
has erect ears about 2^ inches long, and usually contains from
forty to fifty grains in each. The grains are thinner and longer
than those of the two-rowed race, and the awns are stiff and
adhere so firmly to the flowering glume that they are difficult
to remove when thrashed.
Bere is mostly grown in the northern parts of this country as
a spring-sown crop, and used as food for stock and the pro-
duction of whisky. Varieties of this and the six-rowed barleys
are also sown in autumn to be fed off in spring as a green fodder
crop.
On account of its rapid growth and power of giving a moderately
good crop on poor soils, bere is the most suitable cereal for
the northern parts of Europe where the summers are of short
duration ; in such localities it forms the chief bread-stuff.
Formerly this race of barley was used in the preparation of
malt and beer, and to a slight extent this is still the case ; the
proteid-content of the grain is, however, frequently too high
and the starch-content too low for the preparation of a good
malt, and the two-rowed races on account of their superiority
in these respects have now almost entirely superseded bere for
malting purposes. Moreover, on good soil the yield of the two-
rowed varieties is equal to, if not superior to, that of bere.
To this race belong Naked Barley (Hordeum ccclestc L.) and
Himalayan Barley (Hordeum trifurcatum Jacq. **H. ALgiceras
Royle.) (C, Fig. 160). In both of these the caryopses are quite
free from the glumes, and fall out as readily, or more so, than
those of wheat. Himalayan barley is peculiar in having three-
pronged awns which are shorter than the grain, and bend back
in the form of small horns ; it is sometimes termed Nepal wheat,
510 CULTIVATED BARLEYS
the brown 'free caryopses somewhat resembling rather large
pointed wheat grains.
RACE III. Two-rowed Barley (Hordeum sativum distichon
^Hordeum distichon L.) (Fig. 161). In the two-rowed race
only the middle spikelet of each triplet is fertile, the lateral
spikelets being barren (male-flowered); the ear, therefore, possesses
only two longitudinal rows of grain.
This race is the one most commonly grown in the British Isles
and on the Continent, and comprises a considerable number
of sub-races and varieties among which are the finest malting
barleys. When not sufficiently good either in composition or
colour to be used for malting, the grain is a valuable food for
stock.
Several fairly distinct sub-races of Two-rowed Barley are met
with of which the following are the chief:
SUB-RACE I. Peacock, Battledore, Sprat, or Fan Barley,
formerly described as a species, viz., Hordeum Zeocriton L. The
straw is stiff and the ears erect and short, about 2\ inches long,
broad at the base and narrow at the tip (A, Fig. 161). Except
the lower ones of the spike, the grains are thin and of poor
quality, with long spreading awns. The whole ear has a fanci-
ful resemblance to an outspread peacock's tail or fan, hence the
name peacock, fan, and battledore barley applied to it. It is of
little agricultural importance.
SUB-RACE II. Broad Erect-eared Barleys (Hordeum distichon
erectum). In this sub-race the ears are erect and broad, with
plump grains closely packed on the rachis (2?, Fig. 161). The
straw is stiff, and on this account barleys belonging to this sub-
race are useful for growing on somewhat heavily-manured soils
where the danger of ' lodging ' is great for the finer Chevallier
variety.
The grain, although of excellent form and size, usually pos-
sesses a higher proteid-content than is suitable for the production
of the best malt ; nevertheless in exhibitions of making-barley
^\VStv. "'.'.!'-: : r|tf ; ev^ -::; -i
LWw
B-V^-S%^ , 'jt
r^i.^vv
f,^!*^:
f\ i 1 1 - * '*
;#&.,;.-
i: - :1
'rC '.' ' 't., tr ,', " v ,f1
%- J '^V' T -V'i,l
bjt j t ' 4,'i^-t tf t- ;.^
It 4 r ' '
ABC
FlG. 161. Two-rowed Barleys.
A , Sprat or Fan Barley {Hordeum ZeocritoH L.).
2?, Broad erect-eared form (CioldthorpeX
C, Narrow bent-eared form (Chevalhcry
512 CULTIVATED BARLEYS
varieties belonging to this division of the two-rowed race have
not unfrequently taken very high places.
Examples of varieties belonging to this sub-race are, Q-old-
thorpe and Plumage.
SUB-RACE III. Narrow Bent-eared Barleys (Hordeum dis-
tichon nutans). In these barleys the ripe ears bend over on one
side and hang down so as to become almost parallel with the stem.
The ears are narrower and longer than those of the previous
sub-race, the smaller width across the ear being due to the fact
that the grains are placed farther apart on the rachis and jut out
from the latter at a smaller angle than the grains on an erect-
eared variety (C, Fig. 161).
To this sub-race belongs the Ghevallier variety raised by the
Rev. Dr Chevallier from a single ear selected by a labourer in the
parish of Debenham, Suffolk, in 1819.
Chevallier barley and the various selections from it are superior
to all others for malting purposes ; they are, however, somewhat
delicate and liable to lodge on highly-manured soils.
Many other varieties included among nodding-eared barleys
are met with, all of which produce useful malting samples when
carefully managed : common representatives are Old Common,
Nottingham long-ear and others with seedsmen's special names
attached. The grains of these varieties are generally darker in colour
than Chevallier barley, and possess thicker glumes and pericarp.
Plumage-Archer and Sprat- Archer barleys, now widely grown
in Great Britain, are hybrids between varieties belonging to sub-
races II and III. They have stronger straw than Chevallier and
therefore better adapted for growth on soils in high condition.
3. Distinguishing features of barley grains belonging to dif-
ferent races and sub-races. One of the essential conditions for
the production of a good malting sample of barley is that the seed
sown should be as far as possible of the same variety, so that the
ripening of the crop and the composition of the grain should be
uniform. As it is not difficult to distinguish the grains of the chief
races and sub-races from each other, farmers should make a
DISTINGUISHING FEATURES OF GRAINS 513
point of becoming acquainted with their peculiarities, especially
of those belonging to the erect-eared and bent-eared two-rowed
barleys in order to be able to examine samples before purchasing
for seed purposes.
The following are the chief points of difference of the common
races of barley :
(i) The grains of the six-rowed race are elongated, not plump,
with thick glumes ; generally a considerable portion of the base
of the awn is visible on the flowering glume.
Fio. 162. i. Base of grain of bent-eared two-rowed barleys (Chevallier, Old Common, &c.).
3. Diagrammatic longitudinal section of i showing the sloping base. 3. Base of grain of erect-
eared two-rowed barleys (Goldthorpe). 4. Diagrammatic longitudinal section of 3.
The grains of bere are larger and plumper than those of the
typical six-rowed sub-race, but in other respects the two are
similar.
In six-rowed barley and bere the two lateral grains of each
triplet growing at a notch of the rachis are twisted, so that the
two halves of each grain when viewed on the furrow-side are
seen to be dissimilar in size and form ; the presence of these lop-
sided grains in a sample is evidence of their origin.
The middle grains of each triplet are symmetrical on both
514
CULTIVATED BARLEYS
sides of the furrow line and very closely resemble the grains of
the two-rowed races.
(ii) The broad erect-eared barleys, such as Goldthorpe and
Plumage, are easily recognised by the presence of a small deep
transverse furrow across the base of the grain, below which is also
a distinct rounded lump (4, Fig. 162).
The rachilla lying in the longitudinal furrow at the back of the
grain is short and usually bears a number of long thin straight
hairs (3, Fig, 163) : in some varieties of this class, however, the
rachilla is woolly, like i, Fig. 163.
FIG. 163. A, Base of barley grain showing the portion of the rachilla a. landa. RacKilla
of narrow btnt-eared barleys ; i ofChevallicr variety \* of Old Common, Nottingham long-
eared, and many so-called ' Prolific variet es. 3. Rachilla of most broad erect-eared
barleys, c.g Goldthorpe and Imperial varieties; some have rachilla like i.
(iii) The narrow bent-eared barleys have neither transverse
furrow nor lump at the base of the grain, but slope off as at 2,
Fig. 162. Those belonging to the Chevallier stock have a rachilla
which is covered with short wavy wool-like hairs (i, Fig. 163).
The rachilla of the Old Common, Nottingham long-ear, and
so-called ' Prolific ' but inferior malting barleys is longer and the
straight hairs shorter than on the rachilla of the erect-eared
barleys (2, Fig. 163).
4. Characters of a good malting "barley. The following points
are of importance in estimating the suitability of barleys for malt-
ing purposes ; the features of greatest significance are only obtain-
CHARACTERS OF GOOD MALTING BARLEY 5*5
able by chemical analysis, but some of the external and readily
observable characters mentioned below frequently indicate the
value of samples.
a. Composition. In the malting process the starch of the
grain is changed into soluble compounds dextrin and maltose
which are extracted by means of water and ultimately fermented.
The amount of starch should therefore be high in order to obtain
a rich extract ; the best samples contain from 62 to 64 per cent,
of starch.
The proteid-content of barley varies from 6 to over 17 per
per cent. ; it should be as low as possible, as it is found that
barleys with a high percentage of proteids give turbid worts, and
the keeping quality of the beer prepared from them is reduced.
In the best samples the proteids usually average not more than
9 per cent. : medium samples contain 10^ or n per cent., while
poor ones frequently contain 12 per cent.
The amount of water in the grain is important, as it is found
that the drier barleys germinate more quickly and evenly than
the damper samples. Moreover those with a high water-content
sooner lose their germinating capacity and are more liable to be
injured and overrun by saprophytic fungi (moulds) than drier
ones. The amount of water present in the grain depends upon
the ripeness when cut, the method of harvesting, subsequent
sweating in the stack, and upon other conditions. Good samples
contain an average of 14 per cent.
b. Germination Capacity and Germination Energy. The
quicker the germination the more even the malt and the better
the yield of extract. In good samples 96 per cent, of the grains
germinate in seventy-two hours when kept at a temperature of
1 8 to 2oC. ; if the percentage is as low as 85 in this time the
sample should be rejected.
c. Plumpness and Weight. The grains should be short and
thick and of uniform shape, and the sample should be free from
broken grains or those with injured skins. The bushel- weight of
5l6 CULTIVATED BARLEYS
good barleys is 56 Ibs. ; samples exhibited in the Brewers'
Exhibition usually vary from 53 to 60 Ibs. One hundred grains
should weigh between 4 and 5 grams ; in the erect-eared barleys
the latter weight is sometimes exceeded.
d. Mealiness. When cut across the grains should show a
snow-white surface, but rarely do we find samples perfect in this
respect, most of them containing a larger or smaller number
of flinty grains.
e. 'Skin.' The proportion of 'skin' or husk (glumes and
pericarp) to the rest of the grain is subject to much variation ;
in some cases the percentage of husk is as low as 8 per cent, while
in others it is as high as 16. In thin-skinned samples the grains
show a series of delicate transverse lines or puckers due to loss
of water and slight shrinkage of the internal contents during
ripening. Thick-skinned grains show no such lines.
/. Colour. The sample should be pale yellow or a pale
clean straw colour and uniform all over the grain. A stained
or discoloured appearance is often associated with inferior and
damaged samples ; grains, therefore, with brown bases, or which
are grey or of dark tint are to be avoided. The brown tips of
the grains are frequently caused by dark coloured fungi, but
occasionally it is the natural tint of the barley, and may in such
cases be no indication of inferiority of sample.
Barleys exposed to heavy dews and rain are generally darker
in colour than well-harvested crops.
g. Smell. Samples which have been soaked with rain during
stacking often give evidence of the injury by its musty smell.
h. Freedom from broken or cut grains. Great care should be
taken when thrashing malting-barley to have the machine
properly set, so that the awns are not cut off too short nor
the grains cut in two. Closely cut grains often have the
embryo so damaged that the latter will not germinate, and cut
grains are liable to become mouldy when damped and placed on
the making-floor.
CHARACTERS OF GOOD MALTING BARLEY 517
SOIL AND CLIMATE. The northern parts of the country are
usually too wet for the production of mealy grains, but in the
eastern and south-eastern counties of England the best malting
barleys of the world are grown. In hot, dry continental climates
the grain is usually ' thin ' and flinty.
Barley grows most satisfactorily upon light soils; sandy and
calcareous loams free from excess of nitrogenous manures are
best.
SOWING. 'Seed* should be drilled as early as possible in
February or March in order to gife the plant plenty of time
for 4 assimilation ' previous to the building up of a well-nourished
grain.
In some favourable districts barley may be sown in January
but the greater amount is sown in early March.
The amount drilled is from 2 to 3 bushels per acre, the larger
quantity being used on thin soils.
YIELD. The average yield is 32 bushels per acre ; as much as
60 bushels are occasionally obtained.
COMPOSITION. Barley grains contain on an average 14 per
cent of water, 66 per cent, of soluble carbohydrates, loj per
cent, of proteids, and 5 per cent, of 'fibre/
Ex. 262. Examine an ear of six-rowed, four-rowed, and two-rowed barley
respectively.
Observe the arrangement of the spikelets on the rachis and the number
and character of the flowers whether unisexual or bisexual in each.
Ex. 263. Observe at intervals the growth of the caryopsis between the
glumes of a barley floret from the time just after the ear emerges from the
leaf-sheath up to the time when the grain is ripe. Is the caryopsis always
united with the glumes ?
Ex. 264. Cut off the awns from some ears of barley when very young and
compare their growth with those of uninjvrred ears growing near them.
Ex. 265. The student should examine and thoroughly master the details 01
the grains of different races and sub-races of barley.
Note the base of the grain, the rachilla, and also the lodicules of the
flower which are easily dissected from soaked grains.
35
CHAPTER XXXIX.
CULTIVATED RYE (Genus Secale).
i. Characters of the Genus. The inflorescences or 'ears' are
spike-like (Fig. 164), resembling those of wheat in
general structure. The rachis bears two opposite
rows of sessile spikelets.
A single spikelet is placed at each notch of the
rachis, and consists of three flowers, two of which
generally produce grain, the third being in most
cases rudimentary.
The empty glumes are very narrow
and the flowering glumes broad, keeled
from the base, and terminated by a long
awn ; the keel of the glume is fringed
with stiff hairs.
The caryopsis is free from the glumes,
narrower and longer than a wheat grain,
and usually of brownish-olive or greyish- ,
brown tint.
2. Cultivated Rye. Only one species,
namely, Common Eye (Secale cereale
T\- i A j T L c Common Rye.
L.), is cultivated. It appears to be of Empty glume;
more recent origin than the other com- KiumeTrrachni
mon cereals, and is considered to have oflhe ' ear/
arisen from Secale montanum Guss., a species met
with wild in various elevated districts of southern
FIG i6 4 . Ear' and eastern Europe and western Asia.
of Rye (Secale _, . ,. rr
cereakL). The latter species differs from common rye in
618
MIDSUMMER RYE 519
being perennial instead of annual, and in the possession ol
shorter ears and smaller grains.
On the continent, especially in Germany, Russia, Norway,
Sweden, and Denmark, rye forms the principal bread-corn, the
flour of which is made into black-bread. In this country its use
as a bread corn is very limited ; it is, however, extensively grown
as green fodder for sheep and cows, for use in early spring and
summer, and is also cut green for foiling' horses in the stable.
When grown for corn the straw, which is longer than that of
wheat, is practically useless for fodder, but on account of its stiff,
tough character it is well adapted for thatching and litter.
No well-marked races of rye are met with, and the number of
constant varieties is small The latter are characterised only by
differences in yield, tillering power, and hardiness, their morpho-
logical peculiarities being so slight that they furnish no certain
means of distinguishing one variety from another.
The commonest and most useful varieties are those of hardy
constitution, termed Winter Eyes ; in contrast with these are a
few Summer Ryes, which are earlier, less productive, and sown
in spring.
One small-grained variety known as St John's Day or Mid-
summer Rye, possesses extraordinary tillering power, and appears
to be somewhat more nearly allied to the wild species Secale
tnontanum Guss., than the ordinary forms. It is usually sown at
the end of June or beginning of July, and may be fed off with
sheep or cut green in the autumn and following spring, after
which, if left, it will frequently give a good yield of grain.
CLIMATE AND SOIL. Rye is one of the hardiest of cereals,
and is capable of withstanding the severe frost of a continental
winter.
It grows well upon almost all light soils, but especially so upon
such as are sandy ; stiff clays and damp soils rich in humus are
unsuited to its requirements.
SOWING. For corn production the winter rye is drilled at the
520 CULTIVATED RYE
rate of 2 to 3 bushels per acre, usually in September or October,
as early as possible, as tillering goes on chiefly in autumn and
not much in spring.
Summer rye is sown generally in March and April.
When sown for green spring food more seed is sown, usually
from 3 to 4 bushels per acre.
YIELD. The average yield is from 25 to 30 bushels of corn,
and from 30 to 40 cwts. of straw per acre*
COMPOSITION. Rye has practically the same composition as
wheat.
Ex. 266. Examine the various parts of an ear of rye, and compare them
with those of an ear of wheat
CHAPTER XL.
CULTIVATED WHEATS (Genus Triticum).
i. Characters of the Genus. The inflorescences or 'ears* are
spike-like, with two rows of sessile spikelets placed singly at each
notch of the rachis.
The spikelets (Fig. 166) generally possess from two to five
flowers, one or more of the upper ones are always abortive;
usually not more than two or three are fertile and produce ripe
fruits.
The lower spikelets of the * ear ' are often sterile even in the
best selected varieties.
The empty glumes (Fig. 166, e) are broad, thus
differing from rye, and usually have but a short
awn or blunt apex ; the flowering glumes possess
a long or short blunt awn.
The fruit (caryopsis), which is free from the
glumes, has a deep furrow on the back and a hairy
tip ; the colour of the * grain ' may be white, yellow,
let of common 2 ^ g 00( i w h e at grain should be plump, with a
Wheat, t rnipty * *
plume, /flower- smooth, thin, well-filled skin. For the purposes of
mjj glume ; r ra- r r
chi of the ' ear.' the baker it should be somewhat translucent or
semi-glassy when cut across: samples containing many trans-
lucent grains are known on the market as ' strong wheats/ those
with soft floury endosperm being ' weak/
The grains in a sample should also be of uniform colour, size,
and shape.
For sowing the germination rapacity should not be less than
522 CULTIVATED WHEATS
98 per cent, and the weight of 100 grains not less than 4 grams.
The grains should have a hairy tip and the embryo at its base
should be prominently visible through the pericarp; if, on
examination with a lens, the hairs at the tip appear few and
much broken, the sample has most likely been subjected to
rough treatment in order to give it an artificially bright ap-
pearance.
The pericarp of fresh good grain is bright ; in old seed it is
dull; the sample should have neither musty smell nor bad
taste.
3. Cultivated Wheats. With the exception, perhaps, of
Small Spelt and Emmer, none of the cultivated wheats
have been met with in a wild state and their origin is
unknown.
Whether the hundreds of forms in cultivation are the product
of a single species or of several is also not certain.
The following are the chief races or species of cultivated
wheats. (See Percival's Monograph on the Wheat Plant.)
While typical examples of each species are readily distinguished,
transition forms resulting from hybridisation or mutation make
it impossible to define with precision the lines of demarcation
between them.
RACE I. One-grained Wheat or Small Spelt (Triticum
monococcum L.). This race is of pale grass-green colour when
unripe, and possesses a flat, short, compact ear at first sight
resembling two-rowed barley (A, Fig. 167). The spikelets have
two flowers, one of which is abortive; the other produces a single
ripe grain. The flowering glume of the fertile flower bears a
long awn and the straw is stiff and almost solid.
The grain is free from the glumes but does not fall out
when the ear is thrashed; the rachis of the ear is brittle,
and behaves on thrashing as Emmer and Spelt mentioned
below.
One-grained wheat is sometimes cultivated on poor soils in the
r: " :1 ,, 1T t
^r:^
A B C D
FIG. 167. X, Small Spelt (Triticu** ntonococcum L.).
^5, Emmer (Triticttm amyifttm Ser. = 7\ dicoccup* Schub.)
C, Common Spelt or Dinkel (Triticum Sftlta L.)., Bearded.
A Common Spelt or Diokel (Triticum b+tlt* L.), Beardless.
524 CULTIVATED WHEATS
mountainous districts of Spain, Switzerland, and Eastern Europe,
but is of little practical importance.
The yield is from 35 to 35 bushels of spelt grain per
acre.
Small Spelt has doubtless been derived from Triticum agilo-
poidcs Bal., a wild species of grass common in the Balkans and
Asia Minor.
RACE II. Emmer (T. dicoccum Schub.). This race possesses
ears narrow across the face, with the spikelets somewhat
closely packed on the rachis (B, Fig. 167) ; each spikelet
ripens only two grains, and the flowering glumes always have
long awns.
Two-grained spelt is grown in Abyssinia, India, and certain
parts of southern Europe, where it is sown in spring ; its grain
is utilised chiefly for bread and as food for horses.
In this race the grain is free, but so closely invested by
the firm glumes that it does not fall out when the ear is
thrashed. The rachis of the ear is very brittle, and when
thrashed breaks up at each notch where the spikelets are
inserted; the produce after thrashing, therefore, consists of
more or less complete spikelets, to which are attached short
pieces of the rachis.
Emmer has probably been derived from Triticum dicoccoides
Koern, a wild species met with in Syria, Palestine, and western
Persia,
RACE III. Macaroni, Hard or Flint Wheat (Triticum durum
Desf.) (Fig. 1 68, A.). This name is applied to a large number
of spring-sown wheats chiefly cultivated in the Mediterranean
regions and Asia Minor. All the varieties have hard, flinty,
somewhat pointed grains and flattish, empty glumes sharply
keeled to the base ; the flowering glume always has a long awn,
and the straw is stiff, generally solid or filled with pith. The
grain is very rich in gluten, and utilised extensively for making
macaroni.
RIVET, CONE OR TURGID WHEAT 525
RACE IV. Polish Wheat (Triticum Polonicum L.) (C, Fig.
1 68). This race has long ears of glaucous tint when unripe,
and is readily distinguished from all others by its empty glumes,
which are often an inch long and enclose all the flowers in the
spikelet.
In straw, leaf and grain it exhibits close relationship to
Macaroni wheats, and is probably a monstrous form of Race
III.
The flowering glumes are awned and each spikelet contains
four flowers, only two of which are usually fertile.
The c grain ' is f of an inch long and narrow, of reddish
colour, flinty, hard and transparent.
The straw is almost solid.
It is chiefly grown in Spain and Italy.
The yield is too small and the plant too tender for cultivation
in this country.
RACE V. Rivet, Cone or Turgid Wheat (Triticum turgidum
L.) (Fig. 1 68, ). The Rivet or Cone wheats on the Continent
are frequently termed ' English Wheats/ although in England
they are not very much grown.
The ears are large and four-sided with the spikelets
closely packed on the rachis, and the straw yery tall, stiff,
often solid in the upper internodes, and not irt all liable to
lodge.
The empty glumes are somewhat short, inflated and keeled,
and the flowering glume possesses a long awn which often falls
off when the grain is ripe.
The Rivet wheats, of which the author's 'Blue Cone' is a
well-known form, are very late in ripening and only suited to
warm soils in the south of England, where they give very large
yields of grain and long rigid straw of little use except for litter
and thatching purposes.
The grain is short and plump, with a blunt, flattish apex
and a characteristic 'hump' on the dorsal side. It is
A B C
FIG. 168. A, Macaroni Wheat (Triticutn durum Dcsf.).
B, Rivet Wheat, Blue Cone form (Triticunt turgmum L.).
C, Polish Wheat ( Triticum Jolonicum L.).
COMMON WHEAT 527
exceptionally rich in starch and poor in gluten ; the flour is
somewhat dark-coloured and unsuitable for bread-baking ex-
cept when mixed with that from more glutinous varieties of
wheats.
RACE VI. Common Bread Wheat (Triticum vulgare Host.).
To the race of common wheat belong all the most important
varieties in cultivation in the great wheat-growing districts of
Europe, Australia, and America.
The common wheats have empty glumes, keeled only in the
upper half.
Several hundreds of varieties are recorded. Some of the chief
forms grown in this country are mentioned below.
By farmers they are ordinarily grouped, according to the colour
of the grain, into red and white wheats.
Those wheats with white grains require good soils and a dry
warm climate. Such grain often yields flour of good quality, but
the plants are more tender and not so productive as the red-
grained varieties. The latter stand wet winters better than the
white kinds, and are often grown on somewhat inferior wheat
soils.
The presence or absence of awns on the flowering glumes
is the most permanent feature of varieties of wheats. The latter
are, therefore, usually placed in two groups, namely, (i) awnless
or beardless, and (2) awned or bearded varieties. The groups
are then subdivided according to the colour of the glumes
white or red and again according to the smoothness or hairiness
of the glumes.
These may be separated again into types with (i) lax (A and
B, Fig. 169), (2) denser (C, Fig. 169), and (3) compact ears
(Z>, Fig. 169) respectively, and a final division made according
to the colour of the grain.
It is impossible here to mention more than a very few of the
varieties in cultivation, and new ones, or so-called new ones, are
being raised annually. A detailed description, with illustrations
528 CULTIVATED WHEATS
of all those met with in this country at the present time is given
in the author's " Wheat in Great Britain " ; a few of the varieties
widely grown are mentioned below.
SECTION I. Beardless varieties.
a. Glumes white, smooth ; grain white.
(1) Wilhelmina. A somewhat variable sort of winter wheat
with short, dense ears, and plump, white grain of fair quality.
A prolific Dutch wheat selected from a cross.
(2) Victor. A hybrid variety raised by Messrs Carton. It
is a prolific winter wheat, resembling Wilhelmina in some of its
characters.
(3) Starling II. A selection raised by the author from a mixed
stock of Wilhelmina. A high-yielding variety giving fine plump
grain of good milling quality.
Million III and Imperial are varieties also belonging to this
group.
b. Glumes white, smooth ; grain red.
Varieties included in this group are among the most widely
cultivated Bread Wheats.
(;) Bed Marvel, or Japhet. An early sort of wheat originally
produced in France. The straw is somewhat tall and slender,
with long, lax ears. It gives good yields even when sown in
February or early March.
(2) Yeoman. A hybrid winter wheat raised by Sir Rowland
Biffen. It has strong straw, ears of medium density, and grain
1 ' r v v ''r!V" Li "y%i, 1 ^' tj ' i' 1 '.! 1 ^ V ''^Ji- " '^'V'^^Vstf'iiift'.'A^* 11 Lili v-'r ir ''V'
i' h ' ''''ik V",l/ ," ' , r ' '- '' , f- ' n ,, ' r rj 4 ' ,^'lnrTOffa;,,, ,;[!' '-iv' i-'<
A tS *-> ^
FIG. 169. A, B t C k Beardless Bread Wheats (Trilicum vulture Host.).
<4, Lax-eared form.
B, Dense -eared form.
C, ' Squarehead ' form.
O. Beardless Club or Dwaif Wheat (Triticum compactwn Host.).
$30 CULTIVATED WHEATS
of high milling quality. Highly productive on soils in good
condition.
(3) Squarehead. An old variety which first came into pro-
minence about 1870, The name is now given to a number of
winter wheats with short, dense ears and stout straw. All are
prolific varieties, with red grain of fair quality. On account of
weak tillering power they should be sown rather thickly.
Many wheats with new names are selections of the old Square-
head variety.
c. Glumes red, smooth ; grain red.
^i) Little Joss. A hybrid wheat, somewhat variable in colour
of chaff and form of ear, raised by Sir Rowland Biffen. It is an
early sort, which can be sown in autumn or spring up to the end
of February or first week of March. Straw long, with moderately
long, lax ears containing plump grain of fair quality.
(2) Squareheads Master. This is the variety most widely
cultivated in Great Britain at the present time. It is an old
winter wheat which first appeared about 1888-90. The straw
is stout of medium length, with dense well-filled ears containing
brownish red grain of fair milling quality. It is a high yielding
sort which grows well on a variety of soils.
Bed Standard or Standard Red are names given to a variety
of wheat which closely resembles Squareheads Master, and is
possibly a selection of the latter.
SECTION II. Bearded varieties. In these the flowering
glumes have long awns as in Fig. 170. Some of them are hardy,
but most are tender wheats only suitable for spring sowing, and
not much grown in England.
Flo. 170. Bearded Common Bread Wheat (Triticwn vulgare Host.).
A, Lax-eared form.
B. Dense-eared form.
532 CULTIVATED WHEATS
They are usually grouped similarly to the beardless varieties
mentioned above.
April Bearded. A rapid-growing variety, capable of ripening
grain even when sown as late as April or first week of May in
certain favourable localities. It has long, lax ears of reddish
colour. The spikelets often contain four grains, which are light
red and of fair quality.
This variety is apparently a slightly improved form of the Old
Fern Wheat.
In all spring sown varieties the yield is inferior to those sown
in autumn.
CLIMATE AND SOIL. For its full development wheat requires
a warm, somewhat dry, climate.
In hilly districts the plants are small and the yield scanty,
while in wet localities the straw is abundant, but the grain poor
in amount and quality also.
Varieties are met with capable of giving good yields upon
almost all soils except those of the lightest class, and stiff, wet
clays; the soils, however, best suited to growth of the most
valuable wheats are stiff clay loams.
SOWING. Winter wheats are sown in autumn, from September
to December, in this country most frequently in October;
the spring varieties from January to March, most usually in
February.
The seed is drilled in rows from 7 to 10 inches apart, the
amount used varying from i to 3 bushels per acre.
YIELD. The average yield in this country is about 2#|
bushels, but 60 bushels or more per acre are sometimes
obtained; a yield of 40 bushels is usually considered a good
crop.
DINKEL OR LARGE SPELT WHEATS 533
CoMPOsmoN.~-.The composition of the wheat grain varies
much with the climate, soil, manuring, and variety of the plant.
The ' soluble carbohydrates/ mainly starch, average about 66J
per cent. ; the albuminoids, nj ; the ' fibre/ 3 ; the fat, ij ; the
water-content usually about 14 per cent.
The albuminoids in some grains are as low as 8 per cent.,
while in others they may be as high as 24 per cent. ; the flinty
grains are usually richer in this class of substances than the
mealy ones of the same variety of wheat.
RACE VII. Club, Cluster or Dwarf Wheat (Triticum com-
pactum Host.) (Fig. 169, D). The Club wheats usually have
short, stiff straw and exceedingly dense short ears which are rarely
over two inches long ; the empty glumes are keeled in the upper
half and rounded in the lower half.
They are chiefly grown in parts of Germany, Switzerland,
Chili, Turkestan, and the Pacific coastal regions of the
United States. The awned forms are known as ' Hedgehog
Wheats/
The grains of all the varieties are small and plump and yield
flour of moderate quality only.
The Club wheats are closely related to the Common Bread
wheats (T. vulgare).
RACE VIII. Dinkel or Large Spelt Wheats (Triticum Spelta
L.). The varieties of this race have ears with spikelets placed
rather widely apart (C and D, Fig. 167) ; the glumes may be
white, red, or other colours, smooth or velvety, and in some
varieties the flowering glumes are awned, while in others they
are without awns.
The ears possess a brittle rachis which breaks like those of
Emmer and Small Spelt when thrashed. Each spikelet ripens
36
534 CULTIVATED WHEATS
two or three narrow, elongated grains, wliich are triangular in
section.
This race of wheat is cultivated on poor soils in Switzerland,
S. Germany, and Spain. The yield is from 35 to 50 bushels
spelt grain per acre.
Ex. 267. Examine the spikelcts of a ripe ear of common wheat, and note
the number of flowers which have produced well-formed grains, and the
number of abortive flowers.
Ex. 268. If possible obtain specimens of the various species, races, and
varieties of wheat. Note the shape and colour of the caryopsis, the presence
or absence of an awn and keel on the empty and flowering glumes, and
the stiffness, solidity, or hollowness of the internodes of the straw of
each.
Ex. 269. The student should also make a point of examining the general
form of the ears of different common-named varieties of wheat. Measure
how many spikelets are arranged on 2 inches of rachis in each ear. Note
also the colour of the chaff and grain in each.
RECOGNITION OF YOUNG CEREALS BY THEIR LEAVES.
(Examine with a good lens.)
A. Young leaf-sheaths without hairs.
(1) Barley. Base of leaf-blade with two large clasping claw-like
projections as in Fig. 189.
The leaf- blades are very broad with eighteen to twenty-four veins,
and rolled to the right.
(2) Oat. Base of leaf-blade without projections as in Fig. 190.
The leaf-blades are not so broad as those of barley and are a darker
green colour ; they are generally rolled to the left and have eleven
to thirteen veins.
B. Young leaf-sheaths hairy.
(3) Wheat, Young leaf- sheath densely covered with short hairs. The
leaf-blades have claw-like projections intermediate in size be-
tween those of barley and rye ; they are rolled to the right and
have eleven to thirteen veins.
Close to the claw-like projections at the base of the blade are a few
long bristly hairs.
YOUNG CEREALS . 535
(4) Bye. Young leaf-sheaths covered with short hairs among which
are a number of sparsely-scattered long ones easily perceived
with the naked eye.
The first leaf-sheath which comes above ground is a purplish-red
colour ; the blade is rolled to the right and has eleven to thirteen
veins. The claw-like projections are smaller than those of wheat
and the accompanying bristly hairs are shorter and fewer in
number.
CHAPTER XLI.
COMMON GRASSES OF THE FARM.
i . THE Order of Grasses includes a total of over 3000 species,
of which about 130 or 140 are represented in the British
Flora. Many of the species indigenous to this
country are comparatively rare and without any
practical importance to the farmer. The chief
grasses, however, which are met with in most of
the best pastures and meadows are described
below, and a brief mention is also made of those
which require attention on account of their dele-
terious nature as weeds or because of their general
distribution.
Genus Anthoxanthum.
Panicle spike-like ; spikelets one-flowered, flowers
protogynous ; four empty glumes, two lowest un-
equal, smooth, the upper covered with chestnut or
dark brown hairs ; one of them also bears a long,
bent, twisted dorsal awn, the other a shorter,
straight awn; flowering glume, awnless, very
small, smooth; stamens only two.
FIG. 171. Sweet Vernal-Grass (Anthoxanthum odoratum
P aricif P of c sweet L.). A fibrous-rooted perennial, growing about a
uiTTb? 1 *?! B? foot high, and usually present in pastures and
Hguie af c^kSl meadows upon all kinds of soils. It is one of the
(twice natural size). ear ij est g rasse s, often commencing to grow rapidly
in February and March, reaching the flowering stage before the
638
MEADOW FOXTAIL
537
end of April. The leaves are hairy, broad and flat, somewhat
rapidly tapering to a fine long point. The whole plant, especially
when dry, emits a fragrant characteristic perfume, due to a small
amount of coumarin in it ; this pleasant odour it imparts to hay,
in which it is present, and on this account is frequently but
erroneously considered a useful pasture grass. We consider the
inclusion of this grass in mixtures as a serious mistake from
the farmer's point of view, and would strongly recommend the
agriculturist to completely discontinue its use. The yield is in-
significant, and it is refused by almost all kinds of stock when
anything better is to be obtained: moreover,
the price of the seed is always high, and specially
liable to be inferior in quality and purity. Its
place, so far as earliness is concerned, can pro-
fitably be taken on most soils by the far superior
grass, foxtail.
Fuels Vernal-Grass (A. aristatum Boiss. =
A. Puelii Lee. et Lam.) resembles the former
species but its panicle is not so dense and the
stems and leaves more slender and narrower. It
is moreover an annual, and has but a faint odour.
It is a useless weed introduced by * seeds ' used
for the adulteration of those of sweet vernal-grass
(see p. 673).
Genus Alopecurus.
Panicles cylindrical and spike-like, spikelets
one-flowered, compressed, flower protogynous;
empty glumes without awns, fringed with hairs
on the keel and generally more or less united at
their bases ; flowering glume with a bent dorsal
awn, no pale present.
Meadow Foxtail (Alopccurus pratensis L.).
A slightly creeping perennial grass growing best upon damp
and stiffish soils. When sown on dry soils soon dies out. It is
an '% U pjUt
(twice
538 COMMON GRASSES OF THE FARM
one of the best permanent meadow and pasture grasses and
characterised by early and abundant growth. Although it grows
well after being cut, it is best suited for grazing land as its
flowers are shed and its leaves often withered before the time
for cutting grass for hay.
For leys of less than ihree years' duration it cannot be recom-
mended as it is of slow maturation and does not produce its full
yield before the third or fourth year after sowing the seed.
The empty glumes are united about J or J of their length.
Slender Foxtail: Black-Grass (A. myosuroides Huds. =A.
agrcstis L.). An annual resembling the last but distinguished
from it by its longer, more slender, tapering panicles, rougher
stems and its empty glumes, which are united about half their
length. The empty glumes are not so hairy and feel harsher
than those of meadow foxtail, and the flowers are not produced
and ripened till late in summer and autumn. It is a troublesome
pest on arable ground and is also present in small quantity in
pastures and meadows and by waysides in the south of England.
Stock refuse it.
Floating Foxtail (A. genieulatus L.) is another useless species
of this genus common in wet places and near the edges of pools
in damp meadows. Its panicle is i to 2 inches long, slender and
cylindrical, and the stem decumbent and bent at the nodes.
Genus Phleum.
Panicles cylindrical and spike-like : spikelets one-flowered, com-
pressed : empty glumes with short stiff point or awn : flowering
glume membranous, smooth, and awnless.
Timothy : Catstail (1'hleum pratcnse L.). A perennial
growing generally in tufts and often mistaken for meadow foxtail.
Apart from differences in structure it is, however, a much later
grass, and rarely flowers until the spikelets of foxtail begin to fall
from the rachis. Timothy is among the most useful grasses and
can be sown alone or in mixture for leys and permanent pasture.
It is one of the best grasses for heavy clays and produces a large
MARRAM-GRASS I MAT-GRASS
539
bulk of especially heavy hay of high nutritive value. On thin
dry soils, the lower nodes of its stems became thickened and the
whole plant is then of little value.
As it grows hard and fibrous when allowed
to ripen its seed it should be cut before the
spikes are out of the leaf-sheaths. Unlike
foxtail it yields little aftermath. As the seed
is especially cheap and the yield and nutritive
value good, it should form a constituent of all
leys on land which is at all stiff.
Genus Ammophila (Psamma\
Panicles spike-like, spikelets large, one-flow-
ered, compressed : empty glumes two, narrow,
awnless, equal to or just exceeding the flower-
ing glume in length ; flowering glume with
silky hairs at the base and a very short awn.
Marram-Grass : Mat-Grass (Ammophila
arundinacea Host. = Psamma artnaria R.
& S.). A perennial grass which grows on dry
sandy sea-shores. Its stems and leaves are
strong, rigid, and somewhat glaucous, the
former from 2 to 3 feet high ; panicles gener-
ally 3 to 4 inches long, cylindrical.
7 T b .
It possesses an extensive system of rhizomes
which spread through loose sands in all directions, and bind them
into more or less solid banks capable of resisting the action of the
waves. By its action the sea is prevented from encroaching upon
the land, and for this service it is specially protected by Act of
Parliament.
Genus Agrostis.
Panicle spreading ; spikelets one-flowered, very small ; empty
glumes two, unequal, larger than the flowering glume, awnless ;
flowering glume either awnless, or with a slender dorsal awn.
An extensive genus ; most of the species belonging to it are
of little value to the British farmer.
. 11 , .
Spikelct (twice nat-
sue).
540 COMMON GRASSES OF THE FARM
Florin : Marsh Bent-Grass : Red Top (Agrostis alba L.). A
perennial, from 6 inches to 2 feet high, with short, flat, rough
leaves; it is very variable in appear-
ance and habit and met with upon
almost all soils. On drier arable
lands it is as troublesome a pest
as true 'couch,' with which it is
often contused, and in poor, damp
pastures it often abounds
Red Top is one of the most im-
portant perennial pasture grasses
of the United States, but it is not
found on the best pastures and
meadows in this country.
A variety with trailing stems and
B stolons, which take root at the
nodes, is the plant generally re-
ferred to as Fiorin, and named
Agrostis stoloniftra Koch. On re-
claimed bogland, wet meadows,
near river banks, and on moist soils
generally, this variety grows luxuri-
antly and crowds out almost all
other competitors. A special
feature of this grass is its late
autumn growth and power of
remaining green until the following spring.
Fine Bent-Grass : Purple Bent : Black Couch (A. vulgaris
With.=^. ienuis Sibth.). A perennial very similar to the preced-
ing species. It is equally useless except for lawns, for which it is
adapted, as it stands mowing and treading well. Purple bent fre-
quently has purple and reddish stems and leaf-sheaths. It usually
has a short blunt ligule, and the panicle is open when the fruit is
ripe, while Fiorin possesses a long acute ligule, and the branches
of the panicle close up to the main axis when the fruit is ripe,
FIG. 174. A, Panicle of Fiorin or
Marsh Bent-Grass (natural size).
B, Spikelet (twice natural size).
CREEPING SOFT-GRASS
541
This species is known as Rhode Island Bent in the United
States, although this name is sometimes given erroneously to
A. canina (see below).
Brown Bent-Grass (A. canina L.) is another common species
which grows upon wet peaty ground. It has fine, smooth,
narrow leaves, and the flowering glume differs from that of the
other species mentioned in having a long slender dorsal awn.
Genus Holcus.
Panicle spreading; spikelets two-flowered, upper one male,
with awned flowering glume,
lower one bisexual, with awnless
flowering glume; empty glumes
keeled.
Yorkshire Fog: Woolly Soft-
Grass (Holcus lanatus L.). An
extremely common grass about
a foot or 1 8 inches high, with soft
woolly hairs on its leaf-sheaths,
blades, and spikelets. It has a
tufted habit; the awn of the
flowering glume of the male
flower is bentlikeafishhook, and
scarcely visible above the empty
glumes when the seed is ripe.
Creeping Soft - Grass (//.
mollis L.) is similar in general
appearance, but more locally
distributed in the country than
the preceding species. In some
districts it is common, especially on sandy soils and by the side
of shady woods and hedges. It differs from the above by having
somewhat extensive rhizomes, and the awn of the flowering glume
of the male flower is nearly straight
B
FIG. 175.^, Panicle of Yorkshire Fog (na-
, Spfkelet (twice natural sire).
542 COMMON GRASSES OF THE FARM
Almost all hairy grasses are refused by stock, and both these
species are no exceptions to the rule. They produce a
large amount of ' seed ' and often rapidly overrun leys.
In Holland and the eastern counties of England on
damp, somewhat marshy land Yorkshire fog is less
hairy than on drier soils, and is eaten freely by stock :
under these conditions the grass is more palatable, and
animals thrive upon it.
Genus Arrhenatkerum.
Panicle spreading : spikelets two-flower-
ed, the lower flower male, with a flowering
glume possessing a strong bent, twisted
basal awn ; the upper flower is bisexual, with
a short dorsal awn on its flowering glume.
Tall Oat -Grass: French Rye -Grass
(Arrhenatherum avenaceum Beauv. : some-
times named Avena elatior L.). A fibrous-
rooted perennial grass, growing usually
about 3 feet high, and especially common
B in hedges upon light soils. Its spiketets par-
tially resemble those of a small common oat.
Though not always placed in the first class of
fodder grasses, it yields a large bulk of fairly nutritive
produce on marly soils, and begins to grow early in
spring. It stands cutting well, and in some districts
will give two good crops of hay in one season.
The plant has a bitter taste, and when grown alone
stock seem to dislike it at first.
It rapidly attains maturity, often producing a fair
crop the same season as it is sown, but does not last
more than three or four years.
It is sometimes utilised instead of Italian rye-grass
in leys of longer duration than one year.
> A 'bulbous-rooted' variety, in which the
r"n* lower nodes are greatly thickened, is common
natural size), in some localities, and is sometimes known as
< Onion couch.'
(twice
'HASSOCK' GRASS
543
This variety when established on arable land is a troublesome
pest, only satisfactorily eradicated by hand picking.
Genus Deschampsia (Aira).
Panicle spreading; spikelets with two flowers and a rudimen
tary third; empty glumes keeled, unequal, blunt; flowering
glume with a dorsal or nearly basal awn.
Wavy Hair-Grass (Deschampsia flexuosa Trin. ^Airaflexuosa
L.). A perennial grass, growing about 12 to 1 8 inches high, with
very narrow, almost solid,
leaves : common on dry
sandy heaths and pastures.
The branches of the
rachis are often wavy or
flexuous, hence the name.
The spikelets are pur-
plish or brownish green in
colour, and have a shining
silky appearance.
This grass is of no agri-
cultural value, but its * seeds '
are sometimes substituted
for those of golden oat-
grass or used in adulterat-
ing the latter (see p. 677).
Tufted Hair-Grass : * Tus-
sock ' Grass ; * Hassock '
Grass (D. caspitosa Beauv.
= Aira Caspitosa L.). A FIG. 177 A t Panicle of Wavy Hair-Grass
* ' (natural size).
perennial resembling the ** Spikeiet (twice natural size),
previous species in colour of spikelets and several other par-
ticulars. Its leaves are, however, flat, and of leathery texture ;
the awn of the flowering glume is shorter than that of the preced-
ing species, and scarcely exceeds the length of the empty glumes.
B
544 COMMON GRASSES OF THE FARM
It grows in dense tufts, popularly termed ' hassocks ' or ' tus-
socks/ which appear to be raised slightly above the level of the
ground. The most luxuriant development is seen when tufted hair-
grass grows in wet meadows and woods, but its unsightly tufts of
coarse, useless herbage are common on drier meadows and pastures.
B
FIG. 178.^, Panicle of Golden Oat-Grass (natural size). B, Spikelet (twice natural size).
Genus Trisetum.
Panicle spreading ; spikelets two- or three-flowered ; empty
glumes unequal and keeled ; flowering glumes with a somewhat
BRISTLE-POINTED OAT 545
hairy base, two awn-like tips, and a long, bent, twisted dorsal
awn.
Yellow or Golden Oat-Grass ( Trisctum flavescens Beauv. *
Avena flavescens L.). A somewhat creeping perennial
grass, which grows from i to 2 feet high; met with upon
almost all soils, but especially prevalent on those of
calcareous nature. The spikelets are shining and of yellowish
colour.
It is a useful grass, and is liked by all kinds of stock, but the
yield is somewhat small.
The 'seed' is high in price, usually of poor germinating
capacity, and occasionally adulterated with worthless wavy hair-
grass (see p. 677).
Genus Avena.
Panicle spreading ; spikelets with two or more flowers ; empty
glumes, thin, membranous, equalling or exceeding the flower-
ing glumes in length ; flowering glumes stouter, rounded on the
back, with a long, bent, twisted dorsal awn.
Cultivated Oat (Avena sativa L.). (See p. 500.)
Wild Oat (Avena fatua L.). An annual with a large spreading
panicle, probably the origin of the cultivated oat, but differing
from it in the possession of a tuft of reddish yellow hairs at the
base of the flowering glumes (Fig. 155).
It is a troublesome weed among corn crops when once
established.
Bristle-Pointed Oat (Avena strigosa Schreb.) is an annual
much resembling the common cultivated oat, but with smaller
spikelets. It is distinguished from the latter by its flowering
glume being divided, and the tips of the two parts prolonged
into awn-like points or bristles; between these lies the
dorsal awn, the whole glume appearing to possess three
awns.
546 COMMON GRASSES OF THE FARM
It is met with among corn crops, but is rarer than the wild oat.
Two species of Avena, namely, Narrow-leaved Oat-Grass
(Avena pratensis L.) and Downy Oat-Grass (Avena pubescens
Huds.), are perennial grasses growing from i to 2 feet high, and
common in dry pastures, the former especially on calcareous
soils. Neither of them, however, is of any agricultural value,
their produce being small and generally passed over by stock.
Genus Cynosurus.
Panicles spike-like, dense, one-sided : spikelets of two forms,
one completely sterile consisting of several
bristle-like empty glumes arranged alter-
nately on opposite sides of a short rachilla,
the other fertile with three to five flowers ;
flowering glumes of the latter leathery,
three-nerved, with a stiff rigid point.
Crested Dogstail (Cynosurus cristatus
L.). A perennial grass abundant in mea-
dows and pastures throughout the country,
perhaps especially so on the drier upland
sheep walks. We have, however, seen it in a
few damp meadows in exceptional quantity.
After flowering the stems become tough
and wiry : it is therefore not very well
adapted for mowing, but is one of the best
pasture grasses. The short and abundant
leaves, when fresh and young, are very
nutritious and greedily eaten by all kinds
of stock.
The formation of the objectionable and
FIG. i 7 a.A, Spike -like unsightly wiry flowering stems can be
panicle of Crested Dogstail j t j- 11 r
(natural size). avoided by judicious early depasturing of
Bwe of leaf-blade and
feie%!keiet c (SS^lrS It is not very early, and only begins to
natural sue). gj ye j^ g f u u yield two or three years after
COCKSFOOT I ORCHARD-GRASS
547
sowing, so cannot profitably be used in short leys. It should,
however, be included in all mixtures for permanent pastures and in-
cluded in leys of five or six years' duration. It is a good lawn grass.
Genus Dactylis.
Panicle of dense clusters of spikelets all arranged on one side:
spikelets with three to five flowers : empty glumes with a short
rigid point, keeled ; flowering glume keeled, with a short almost
terminal >tiff rough awn.
Cocksfoot : Orchard-Grass (Dactylis glomerata L.). One
of the commonest of all grasses
perennial, with a strongly - tufted
habit of growth. Its leaf-sheaths
are flattened and blades large and
flat. It is met with upon all soils,
and ranks in the first class of forage
grasses on account of its heavy
yielding power, high nutritive quality,
and power of rapid growth after
being cut. Cocksfoot is one of the
first grasses to spring up after a field
is mown. It is, however, not well
adapted for meadows for hay as its
unsightly tufts become coarse and
woody if allowed to grow until the
remainder of the grasses are ready
to cut.
Pastures in which Cocksfoot is
abundant should be kept well grazed.
It is slow to mature, and should not
be used for leys of shorter dura-
tion than three or four years ; but
in mixtures for longer leys and per- *
manent pasture it should always be
included in moderate amount.
- B A
FIG. 1 80.^, Panicle of Cocksfoot
. and ii ?u ie.
c > Splkclet (twicc natural S12C) -
548 COMMON GRASSES OF THE FARM
Genus Poo.
Panicles spreading; spikelets compressed, with two to six
flowers ; rachilla often * webbed ' or clothed with woolly tangled
hairs ; empty glumes shorter than the flowering glumes ; flower-
ing glume keeled the whole length, awnless.
Annual Meadow-Grass (Poa annua L.). A very common grass
on all soils, and especially noticeable when on waste ground. It is
annual, and met with in flower during almost every month in the
year. The rachilla is not webbed. Stems about 6 to 1 2 inches
long often lying close to the ground. It possesses little
agricultural value, although stock eat the early growth with
avidity.
Smooth-stalked Meadow-Grass : Kentucky Blue-Grass (Poa
pratcnsis L.). A common perennial grass with well-developed
rhizomes and smooth stems above ground from 12 to 15 inches
high. Rachilla webbed; flowering glume with five nerves,
three of them hairy. Upper leaf-sheath longer than the
blade, the ligules of the leaves short and blunt. It is an
excellent bottom grass and especially suited to the lighter and
medium soils. This meadow grass commences to grow early
in spring, but produces only a moderate aftermath when cut
for hay.
Flat-stemmed Meadow-Grass: Canada Blue-Grass (Poa
comprtssa L.) resembles P. pratcnsis, with flattened stems and
compressed shoots decumbent at the base and rhizomatous.
The upper leaf-sheath is about equal in length to the blade, the
rachilla webbed, the flowering glume with three hairy nerves.
It is found on dry banks and walls, and adapted for sandy
and arid soils ; in Canada it grows on poor clay where better
grasses do not succeed.
Rough-stalked Meadow-Grass (Poa trivialis L.).- A common
perennial much resembling the preceding species. It has, how-
ever, no long rhizomes. The stems are somewhat rough, the
LATE MEADOW-GRASS
549
upper leaf-sheath longer than the blade, the ligule long and
pointed. Rachilla webbed; flowering glume five-nerved, only
the central nerve hairy. It is one of the best ' bottom ' grasses,
and is to be preferred before all others for sowing on the stiffer
and damper class of soils in sheltered situations. It is less hardy
than smooth - stalked meadow-
grass, suffering more readily from
frost and drought, and does not
start growth so soon in spring.
Wood Meadow - Grass (Poa
ntmoralis L.). A perennial grass
resembling the three previous
species, but with more slender
stems, and generally confined to
shady places and woods. It has
narrow leaves, the sheaths not
longer than the blades, and a
very short ligule. Rachilla
webbed, flowering glume with
five nerves, three of them hairy.
Although it will endure a certain
amount of drought when grown
in the open meadow, its practical
agricultural value is small.
Late Meadow - Grass (Poa
palustris Z. P. serotina Ehrh.) is
not a native British species, but its seeds are sometimes sold in
place of those of the two previous species. It is a coarse, tufted
kind of Poa adapted for growth in marshy places, where it yields
a good late crop of grass.
Genus Festuca.
Panicles usually spreading; spikelets with three or more
flowers; empty glumes unequal, shorter than the flowering
37
FIG. 181. A> Panicle of Rough -stalked
Meadow-Grass (natural size).
B % Spikekt (twice natural size).
550 COMMON GRASSES OF THE FARM
glume; lower half of the flowering glume rounded on the back,
upper part often keeled, awned from the tip or with a short, stiff
point ; styles terminal on the ovary.
Meadow Fescue (Ftstuca pratensis Huds.). A perennial broad,
flat-leaved grass grow n^ iiom 2 to 3 feet high, and common in
damp meadows. Although somewhat
tufted in habit it tends to cover the
ground very evenly. It is among the
earliest of grasses to start growth in
spring, often rivalling meadow foxtail
in this respect. It yields a large
amount of nutritious fodder and grows
rapidly after mowing or depasturing with
stock.
Meadow fescue produces its full yield
only after three years growth from the
seed, and is therefore most suited for the
longer leys and permanent pasture.
Tall Fescue (Fcstuca elatior L.) re-
sembles the last species but is more
tufted in habit, and its leaves, stems,
and other parts are larger and of coarser
texture. It is met with on river banks
and in wet places generally, where it
frequently grows to a height of 4 or
5 feet. Although it is eaten by all
kinds of stock its coarseness unfits it
for use in leys and permanent pasture.
Possibly meadow fescue is merely a
ciiKsneriVs of this nlant
SUDS PedeS OI IHIS piam.
Fest'tca arundinacea Schreb., which
grows near the sea coast in many parts
of the country, is a large form of tall fescue with rough leaf-
sheaths.
Meadow Fescue (natural ->ize).
By Spikclet (twice natural
size).
RED FESCUE
5SI
Sheep's Fescue (Festuca ovina L.). A small perennial grass,
usually not more than a few inches high and growing in tufts,
with narrow, almost solid, bristle-like leaves and smooth leaf-
sheaths. It grows well on dry soils, and is
one of the chief constituents of upland sheep
pastures.
A variety of fine-leaved sheep's fescue (F.
ov. var. tenuifolia Sibth.) has almost awnless
spikelets.
Hard Fescue (Festuca duriuscula L.) resembles
the last species, but has narrow, flat leaves,
downy leaf-sheaths, a more open panicle, and
does not grow in such dense tufts. It is also
of larger growth than sheep's fescue.
Both these grasses are constituents of the
best sheep pastures on the higher ground of
this country, and are almost unaffected by the
driest weather. Their produce is small but
nutritious and more succulent than the general
appearance of the leaves indicates. Hard
fescue may be used with advantage, in
moderate amount, as a 'bottom' grass in
all mixtures for permanent pasture in dry
situations.
Red Fescue (Festuca rubra L.) is a perennial
grass very nearly related to the last two species. sh y in g
o / / f Action and manner
It possesses narrow, flat leaves, pale red of folding,
spikelets, and creeping rhizomes.
The limits of the last three species of Festuca are ill-defined,
as a large number of varieties exist which are intermediate in
character between them.
Little or no attempt is ma'e by seedsmen to supply 'seeds'
of these species true to name, and for practical purposes there is
no necessity to do so.
Sheep's Fescue (nat-
ural size).
B. Base of leaf-
blade and piece of
stem
A, Piece of leaf
552 COMMON GRASSES OF THE FARM
Genus Bromus.
Panicles spreading : spikelets large with five or more flowers :
empty glumes, unequal, acute : flowering glume generally with a
divided tip and an awn which arises just below the tip. Styles
lateral on the ovary.
An extensive genus of coarse, harsh or hairy-leaved grasses,
the species of which are nearly all useless or of small importance
as forage plants.
Awnless Brome-Grass : Hungarian Forage-Grass (Bromus
tnermis Leyss.). A tall perennial grass with long rhizomes and
smooth leaves sometimes over half an inch broad. It is grown
extensively in Hungary, and the north-western United States,
alone or in mixture with lucerne, on dry soils where it gives very
large yield of grass, which if cut early makes fairly nutritious
hay.
It grows slowly in spring, but two cuts are often secured
on the Continent in one season when the plant is thoroughly
established.
Our experience with it in this country has not been successful
even on the looser soils, for which it has been specially recom-
mended.
Rescue Grass: Schroder's Brome-Grass (Bromus unioloidcs
H. B. K. = B. Schraderi Kunth.). An annual or biennial grass
with harsh broad leaves, recommended sometimes on account
of its productiveness on thin soils.
It is a native of South America, and grown for forage in warm
climates.
After several years' trial we cannot advise its being grown by
the British farmer, as it rapidly becomes coarse, grows in massive
tufts, and is liable to die off in winter and become patchy in the
second or third year after sowing.
Soft Brome-Grass (Bromus mollis L.). An annual or biennial
grass very common on dry roadsides and waste places and
growing about a foot high. It has thin broad leaves, the
RYE-LIKE BROME-GRASS
S53
sheaths and blades of which are soft and downy ; the spikelets are
also covered with soft hairs. It is a pest of temporary pastures.
Somewhat similar is Bromus raccmosus L. with glossy, almost
smooth, spikelets and
slightly hairy leaves.
Field Brome-Grass (B.
arvensis L.) is an intro-
duced grass from i to
2 feet high with wide
spreading panicle and long,
narrow, drooping spikelets
usually of violet-brown
tint. It is sometimes grown
in Sweden and other
countries for green fodder
or hay, though in this
country considered a weed
of corn crops. Rye-like
Brome-Grass (B. secalinus
L.) is a troublesome weed
of corn-crops.
Genus Brachypodium*
Panicles spike-like, the
cylindrical spikelets have
very short stalks, and are
arranged on opposite sides
oftherachis. Eachspikelet
possesses five or more
flowers : empty glumes
two : flowering glume with
a terminal awn. A small
genus of harsh perennial useless grasses.
British species, namely :
B
FIG. 184. /4, Panicle of Soft Brome-Grau
(natural sue).
B % Spikelet (twice natural sue).
There are two
554 COMMON GRASSES OF THE FARM
False Brome-Grass (Brachypodium pinnatum Beauv.), Fig. 256,
and Slender False Brome-Grass (Brachypodium sylvaticum R.
and S.). The farmer species has an erect panicle and is
common on open downs and poor pastures in chalky
districts : it is known as ' Tor grass ' in Kent. The
latter species has a drooping inflorescence, and is met
with in woods and on hedge-banks.
Genus Nardus.
Inflorescence a spike : spikelets one-flowered arranged
one at each notch of the rachis, and on one side of the
latter: no empty glumes : flowering glume narrow with
a short awn.
Mat-Grass (Nardus stricta L.). A small stiff peren-
nial grass 6 or 8 inches high. Common on dry heaths
and moors. Its stems and leaves are wiry and rejected
by sheep.
Genus Hordeum.
Inflorescence a spike : spikelets one-flowtred arranged
three together at each notch of the rachis and alter-
nately on opposite sides of the latter. All three
spikelets at each notch may be bisexual or only the
central one, the lateral spikelets being in the latter case
male or neuter : empty glumes two, very narrow, awned,
placed partially in front of the spikelet. Flowering B ^
glume with a long terminal awn. FIG. 185.
Cultivated Barley (Hordeum sativum Pers.). (See M'at ?Gras S
' ^ (Nardus
P. 506.) strida L.)
Meadow Barley (Hordeum pratense Huds.). A per- s?ze)! ura
... . . /Mtaseof
ennial species common m wet or damp meadows near leaf- blade
riversides where it grows about 18 inches high. a " lgu e *
It possesses a slender stem and narrow flat leaves. Meadow
barley grows early in spring and may be considered a useful
pasture grass when not allowed to flower. In hay, however,
PERENNIAL RYE-GRASS : RAY GRASS 555
the awns of the spikelets are irritating and injurious to
stock.
Wall Barley (Hordeum murinum L.). An annual much re-
sembling meadow barley, but met with on dry waste ground and
about footpaths and roadsides near walls.
It is not so tall as meadow barley, and is of no agricultural
value.
Genus Lolium.
Inflorescence a spike ; one spikelet at each notch of the
rachis ; the spikelets are many-flowered,
and are inserted so that they stand in
the median line of the rachis, that is, the
plane passing through the middle of the
glumes passes through the rachis also.
The terminal spikelet has two empty
glumes, the lateral spikelets only one
(the outer empty glume) ; flowering
glume awned or awnless.
Perennial Rye-Grass : Ray Grass
(Lolium perenne L.). A perennial
common in all the best pastures and
meadows throughout the country, and
used probably more extensively than
any other grass in mixtures for leys and
permanent pastures.
The leaves are folded in the bud,
and the flowering glumes awnless.
It grows most luxuriantly on soils
which are loamy or stiffish in char-
acter. On dry soils the produce is
FIG iSfi.-^, Spike of Perennial Sma11 and f Httle VaUlC -
^S^onSSudTidiign^ , Perennial rye-grass is a variable
B, Spikelet of Italian Rye-Grass, plant, and manv varieties are met with
(twte C c C naturai c K ial Rye " differing chiefly in yield, fineness of
leaf, den